Charged particle beam exposure system and method

ABSTRACT

A charged particle beam exposure method includes the steps of creating dot pattern data indicative of a pattern to be exposed, storing the dot pattern data in a first storage device having a first access speed, transferring the dot pattern data from the first storage device to a second storage having a second, higher access speed, reading the dot pattern data out from the second storage device, and producing a plurality of charged particle beams in response to the dot pattern data read out from the second storage device by means of a blanking aperture array, wherein the blanking aperture array includes a plurality of apertures each causing turning-on and turning-off of a changed particle beam pertinent to the aperture in response to the dot pattern data.

BACKGROUND OF THE INVENTION

The present invention relates to charged particle beam exposure systemsand methods and more particularly to a charged particle beam exposuresystem and method for exposing a desired pattern on a surface of anobject as a result of raster scanning of charged particle beams, whilecontrolling each of the plurality of charged particle beams such thatthe charged particle beams as a whole form a beam bundle having thedesired exposure pattern.

The present invention uses some of the teachings of the U.S. Pat. No.5,369,282 and the U.S. patent application Ser. No. 08/241,409 filed May11, 1994, which are incorporated herein as reference.

With the advancement in the art of fine lithographic patterning, recentintegrated circuits are formed with such a high integration density thatthey are now used commonly and widely in industries including computers,telecommunications, system control, and the like. Looking back thehistory of dynamic random access memories, for example, it will be notedthat the dynamic random memories have increased the integration densityas represented in terms of storage capacity of information, from 1 Mbitsto 4 Mbits, from 4 Mbits to 16 Mbits and from 16 Mbits to 64 Mbits.Currently, dynamic random access memories having a storage capacity of256 Mbits or 1 Gbits are studied intensively. In correspondence to suchan increase in the integration density, extensive studies are inprogress for developing the art of so-called charged particle beamexposure that use a charged particle beam such as an electron beam forexposing fine patterns on an object. By using such a charged particlebeam, it is possible to expose a pattern having a size of 0.05 μm orless, with an alignment error of 0.02 μm or less.

On the other hand, conventional charged particle beam exposure systemshave suffered from the problem of low throughput of exposure, and therehas been a pessimistic atmosphere prevailing among the skilled artisanin the art about the production of integrated circuits by means of sucha charged particle beam exposure system. It should be noted that theconventional charged-particle-beam exposure systems have used a singlecharged particle beam for the exposure and it has been necessary to drawa desired pattern on the object such as a substrates by a single strokeof the charged particle beam.

On the other hand, most of such pessimistic observations addressingnegative prediction about the future of charged-beam-exposure system andmethod, are not well founded, as is typically demonstrated by theinventors of the present invention who have succeeded in constructing ablock exposure system and a BAA (blanking aperture array) exposuresystem that provide a throughput of as much as 1 cm² /sec. With the highthroughput of 1 cm² /sec thus achieved, the main disadvantage of thecharged-particle-beam exposure system and method is substantiallyeliminated. Now, it is thought that the charged-particle-beam exposuresystem and process are superior to any other conventional exposuresystems in terms of high resolution, small alignment error, quick turnaround time, and reliability.

As already noted, it is particularly essential for acharged-particle-beam exposure system to have a high exposurethroughput, and block exposure process or BAA process has been developedfor clearing the requirement of high exposure throughput. Hereinafter, aBAA exposure system proposed previously by the inventors of the presentinvention will be described briefly. For the sake of simplicity, thedescription hereinafter will be made for an electron beam exposuresystem, while the present invention is by no means limited to anelectron beam exposure system but is applicable to any other chargedparticle beam exposure systems such as an ionic beam exposure systemthat uses a focused ionic beam.

In a BAA exposure system, a plurality of electron beams are producedsuch that the plurality of electron beams as a whole form a desiredelectron beam bundle with a shape corresponding to a pattern to beexposed on an object. Thereby, each of the plurality of electron beamsis turned on and off individually according to the desired pattern to beexposed. Thus, each time the exposure pattern is changed, different setof electron beams are turned on. While being exposed by the electronbeams on the object, which may be a substrate, the object is moved,together with a stage on which the object is supported while deflectingthe electron beams back and forth by activating a deflector.

In order to produce the foregoing plurality of electron beams, the BAAexposure system employs a BAA mask that is a plate formed with a numberof rectangular apertures arranged in rows and columns for shaping asingle electron beam incident thereto. Each of the apertures carries apair of electrodes on opposing edges, wherein one of the electrodes isset to a ground potential level while the other of the electrodes issupplied with a control signal that changes the level between the groundlevel and a predetermined energization level. In response to theenergization of the electrodes on the BAA mask, the path of the electronbeam through the aperture is deflected and the arrival of the electronbeam upon the object is controlled accordingly. In other words, theelectron beams are turned on and off on the object in response to thecontrol signal applied to the electrodes of the apertures on the BAAmask. It should be noted that the control signals applied to theapertures on the BAA mask represent a pattern of the electron beamsproduced by the BAA mask, and the control signals are changed insynchronization with a raster scanning of the surface of the object bythe electron beam bundle. As a result of the raster scanning, the objectis exposed along a band or zone.

In such conventional BAA exposure systems and methods, there are stillvarious problems to be overcome, such as further improvement of theexposure throughput including improvement of data transfer rate and datacompression, improvement in the precision of the exposed patternsincluding optimization of exposure dose and improvement of resolutionwhen expanding exposure data into bit map data, uniform distribution ofthe electron beam intensity throughout the substrate, improved dataprocessing such as expansion and transfer of the exposure dot data,positive on-off control of the electron beam, easy maintenance of theBAA mask, exposure of large diameter wafers, improvement of electronoptical systems, and easy switching between a BAA exposure mode and ablock exposure mode, and the like.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a noveland useful charged-particle-beam exposure system and method wherein theforegoing problems are eliminated.

Another and more specific object of the present invention is to providea charged-particle-beam exposure method and system for exposingversatile patterns on an object by means of a charged particle beam thatforms an exposure dot pattern, in which the creation of dot pattern datarepresenting the exposure dot pattern and the exposure of the object bymeans of the charged particle beam can be achieved separately.

Another object of the present invention is to provide acharged-particle-beam exposure method and system that is capable ofholding a large amount of dot pattern data representing the exposure dotpattern and that can control a blanking aperture array based upon thedot pattern data at a high speed for producing a charged particle beambundle including a number of charged particle beams in correspondence toeach dot of the exposure dot pattern.

Another object of the present invention is to provide a method forexposing a pattern on an object by means of a charged particle beam,comprising the steps of:

shaping a charged particle beam into a plurality of charged particlebeam elements forming collectively a charged particle beam bundle havinga desired pattern in response to exposure data;

calculating a beam correction to be applied upon said charged particlebeam elements for compensating for a beam distortion when exposing saiddesired pattern on said object, as a function of said exposure data,said step of calculation being conducted in response to a correctionclock; and

exposing said desired pattern upon said substrate by radiating saidcharged particle beam bundle upon said object in response to an exposureclock;

said step of exposing comprising the steps of:

setting a frequency of said exposure clock based upon a sensitivity of aresist provided on said object and a current density of said chargedparticle beam elements; and

emitting said charged particle beam elements forming said chargedparticle bean bundle upon said object in response to said exposureclock, with said bean correction applied to said charged beam elements;

wherein said correction clock is synchronized to said exposure clock andheld at a substantially constant, predetermined frequency when changingthe frequency of said exposure clock in said step of setting thefrequency of said exposure clock.

Another object of the present invention is to provide a charged particlebeam exposure system for exposing a desired pattern on an object,comprising:

a charged particle beam source for producing a charged particle beam andemitting the same along a predetermined optical axis;

beam shaping means provided on said optical axis so as to interrupt saidcharged particle beam, said beam shaping means carrying thereon aplurality of apertures for shaping said charged particle beam into aplurality of charged particle beam elements collectively forming acharged particle bundle, each of said apertures carrying switching meansfor selectively turning off said charged particle beam element inresponse to exposure data;

beam focusing means for focusing each of said charged particle beamelements forming said charged particle beam bundle upon said object;

deflection means for deflecting said charged particle beam elementscollectively over a surface of said object in response to a deflectioncontrol signal supplied thereto;

deflection control means supplied with deflection data for producingsaid deflection control signal;

beam correction means for calculating a beam correction to be applied tosaid electron beam element as a function of said exposure data forcompensating for a beam distortion, said beam correction calculationmeans carrying out said calculation in response to a correction clock;

exposure control means for conducting an exposure of said chargedparticle elements in response to an exposure clock; and

clock control means supplied with control data indicative of a currentdensity of said charged particle beam elements and a sensitivity of saidelectron beam resist, for producing said exposure clock and saidcorrection clock, such that said exposure clock has a clock speeddetermined as a function of said control data, said clock control meansfurther holding said correction clock substantially constant at apredetermined frequency irrespective of the frequency of said exposureclock.

According to the present invention, it is possible to conduct thedevelopment of exposure data into exposure dot data and the exposure ofthe pattern on the object at respective timings. Thereby, the exposurethroughput is no longer limited by the data expansion of the exposuredata to the exposure dot data and a high exposure throughput can beachieved. Further, it is possible to hold or save a large amount ofexposure dot data in the primary storage device that may be a hard diskdevice. By using a non-volatile storage device such as a hard disk forthe primary storage device, it is possible to examine the exposure datain the form of exposure dot data. Further, such exposure dot data can beused repeatedly in the production of a semiconductor device. Althoughthe primary storage device may have a limited access speed, it should benoted that the exposure dot data is supplied to the beam shaping means,which is a blanking aperture array, at high speed from the secondarystorage device.

In a preferred embodiment of the present invention, two or more highspeed memory devices are used for the secondary storage device eachhaving a storage capacity smaller than the primary storage device.

Another object of the present invention is to provide a charged particlebeam exposure system and method wherein a high precision exposure isguaranteed even when the setting for the current density of the electronbeam or the sensitivity of the electron beam resist is changed.

Another object of the present invention is to provide a method forexposing a pattern on an object by means of a charged particle beam,comprising the steps of:

shaping a charged particle beam into a plurality of charged particlebeam elements forming collectively a charged particle beam bundle havinga desired pattern in response to exposure data;

calculating a focusing error correction and an aberration correction tobe applied upon said charged particle beam elements when exposing saiddesired pattern on said object, as a function of said exposure data,said step of calculation being conducted in response to a correctionclock; and

exposing said desired pattern upon said object by radiating said chargedparticle beam bundle upon said object;

said step of exposing comprising the steps of:

setting an exposure clock speed based upon a sensitivity of an electronbeam resist provided on said object and a current density of saidcharged particle beam elements; and

emitting said charged particle beam elements forming said chargedparticle beam bundle upon said object in response to said exposureclock, with said focusing error correction and said aberrationcorrection;

wherein said correction clock is held in the vicinity of a predeterminedclock speed when changing a clock speed of said exposure clock in saidstep of setting the exposure clock speed.

Another object of the present invention is to provide a charged particlebeam exposure system for exposing a desired pattern on an object,comprising:

a charged particle beam source for producing a charged particle beam andemitting the same along a predetermined optical axis;

beam shaping means provided on said optical axis so as to interrupt saidcharged particle beam, said beam shaping means carrying thereon aplurality of apertures for shaping said charged particle beam into aplurality of charged particle beam elements collectively forming acharged particle bundle, each of said apertures carrying switching meansfor selectively turning off said charged particle beam element inresponse to exposure data;

beam focusing means for focusing each of said charged particle beamelements forming said charged particle beam bundle upon said object;

deflection means for deflecting said charged particle beam elementscollectively over a surface of said object in response to a deflectioncontrol signal supplied thereto;

deflection control means supplied with deflection data for producingsaid deflection control signal;

beam correction means for calculating a correction to be applied to saidelectron beam element as a function of said exposure data, said beamcorrection calculation means carrying out the calculation in response toa correction clock;

exposure control means for conducting an exposure of said chargedparticle elements in response to an exposure clock; and

clock control means supplied with control data indicative of a currentdensity of said charged particle beam elements and a sensitivity of saidelectron beam resist, for producing said exposure clock and saidcorrection clock, such that said exposure clock has a clock speeddetermined as a function of said control data, said clock control meansfurther holding said correction clock substantially constantirrespective of said exposure clock.

According to the invention of the present embodiment, one can guaranteea necessary exposure dose by changing the exposure clock as a functionof the resist sensitivity and the current density. On the other hand,the analog signal supplied to the deflection means, which includes amain deflector and a sub-deflector, changes generally linearly withtime, and the problem of the exposure beam failing to hit the desiredpoint on the substrate is effectively eliminated.

Another object of the present invention is to provide a charged particlebeam exposure system and method that is capable of exposing an object bycharged particle beams produced by a BAA mask with a uniform electronbeam intensity irrespective of the location of the apertures on the BAAmask that are used for shaping the electron beams.

Another object of the present invention is to provide a method forexposing a pattern on an object, comprising the steps of:

shaping a charged particle beam into a plurality of charged particlebeam elements forming collectively a charged particle beam bundle havinga desired pattern in response to exposure data;

exposing a desired pattern upon said object by radiating said chargedparticle beam bundle upon said object;

said step of beam shaping comprising the steps of:

activating a plurality of apertures provided on a beam shaping mask forshaping said charged particle beam, such that a predetermined number ofsaid apertures are activated each time as a unit, each of said aperturesincluding a deflector for deflecting a charged particle beam elementpassing therethrough in response to an activation of said aperture, saidpredetermined number of apertures thereby producing a plurality ofcharged particle beam elements equal in number to said predeterminednumber; and

detecting the intensity of said predetermined number of charged particlebeam elements on said object;

said step of activating said plurality of apertures being conducted suchthat the intensity of said charged beam elements, produced as a unit, isequal to the intensity of said charged particle beam elements of otherunits, by optimizing an energization of said deflectors on saidpredetermined number of apertures.

Another object of the present invention is to provide a charged particlebeam exposure system for exposing a pattern on an object, comprising:

a charged particle beam source for producing a charged particle beam andemitting the same along a predetermined optical axis;

beam shaping means provided on said optical axis so as to interrupt saidcharged particle beam, said beam shaping means carrying thereon aplurality of apertures for shaping said charged particle beam into aplurality of charged particle beam elements collectively forming acharged particle bundle;

switching means for selectively turning off said charged particle beamelement in response to a control signal;

driving means for driving said switching means on said beam shapingmeans by supplying thereto said control signal in response to exposuredata;

beam focusing means for focusing each of said charged particle beamelements forming said charged particle beam bundle upon said object;

detection means for detecting the intensity of said charged particlebeam elements on said object;

correction means for controlling said driving means such that saiddriving means supplies said control signal to said switching means withan offset added thereto, said correction means evaluating said offset inresponse to the intensity of said charged particle beam elementsdetected by said detection means, such that a group of charged particlebeam elements including a predetermined number of charged particle beamelements therein has an intensity that is substantially identical to theintensity of other charged particle beam elements forming other groups,each of said other groups including said charged particle beam elementsin number identical to said predetermined number.

According to the present invention as set forth above, the intensity ofthe charged particle beam elements is detected for each unit or groupincluding a predetermined number of charged particle beam elements,wherein the intensity of the charged particle beam elements is adjustedfor each unit in response to the detected beam intensity on the object,by adjusting the energization of the switching means or deflectorscooperating with each of the apertures, such that the beam intensity issubstantially uniform over the entire surface of the object. Thereby,the problem of the exposure dots shaped by the apertures on the marginalarea of the BAA mask is substantially eliminated, and a high precisionexposure becomes possible.

Another object of the present invention is to provide a charged particlebeam exposure system and method that improves the data transfer rate andhence the exposure throughput by compressing the dot pattern data duringthe process of data transfer.

Another object of the present invention is to provide a method forexposing a pattern on an object by means of a charged particle beam,comprising the steps of:

producing a plurality of charged particle beam elements in the form ofdot pattern data, said plurality of charged particle beam elements beingproduced simultaneously as a result of shaping of a single chargedparticle beam by a mask, said mask carrying a plurality of beam shapingapertures arranged in rows and columns on a mask area;

focusing said plurality of charged particle beam elements upon anobject; and

scanning a surface of said object by means of said plurality of chargedparticle beam elements in a first direction;

said step of producing the plurality of charged particle beam elementsincludes the steps of:

dividing said dot pattern data into a plurality of data blocks eachcorresponding to a rectangular area on said beam shaping mask, saidrectangular area having a size in a second direction perpendicular tosaid first direction such that said size is smaller than a size of saidmask area in said second direction;

providing identification codes to said data blocks for discriminatingsaid data blocks from each other, such that identical data blocks havean identical identification code;

storing said data blocks respectively in corresponding dot memories,together with said discrimination codes corresponding to said datablocks;

reading out said data blocks from said dot memories consecutively byspecifying said identification codes consecutively; and

shaping said single charged particle beam by said beam shaping mask intosaid plurality of beam shaping beam elements in response to said datablocks read out from said dot memories.

Another object of the present invention is to provide a charged particlebeam exposure system for exposing a pattern on an object, comprising:

beam source means for producing a charged particle beam and for emittingthe same along an optical axis in the form of a charged particle beamtoward an object;

beam shaping means disposed on said optical axis so as to interrupt saidprimary charged particle beam, said beam shaping means carrying on amask area thereof a plurality of apertures each supplied with exposuredot data representing a dot pattern to be exposed on said object, saidapertures thereby shaping said charged particle beam into a plurality ofcharged particle beam elements in response to said exposure dot data,said plurality of charged particle beam elements as a whole forming acharged particle beam bundle;

focusing means for focusing each of said charged particle beam elementsin said charged particle beam bundle upon said object with ademagnification;

scanning means for scanning a surface of said object by said chargedparticle beam elements in a first direction;

a dot memory for storing dot pattern data for data blocks eachcorresponding to a group of exposure dots to be formed on a rectangulararea on said object, said rectangular area having a size on said object,in a second direction perpendicular to said first direction, to be equalto or smaller than a size of said mask area projected upon said objectand measured in said second direction;

a code memory for storing codes each specifying one of said data blocks;

block addressing means for addressing, based upon said codes read outfrom said code memory, said dot memories consecutively from a firstaddress to a last address of a data block specified by said code; and

code memory control means for reading said codes from said code memoryconsecutively in the order of exposure.

According to the present invention set forth above, the same exposuredata is used repeatedly by specifying the codes. It should be noted thatthe same data block has the same code. Thereby, the amount of the dotpattern data is substantially reduced. It should be noted that such areduction in the amount of data decreases the duration of data transfer,and the throughput of exposure is improved substantially.

Another object of the present invention is to provide a charged particlebeam exposure method and system that are capable of exposing a patternon an object at a high speed, without requiring particular dataprocessing with respect to pattern width or contour of the exposedpattern when conducting a minute adjustment of the exposed pattern.

Another object of the present invention is to provide a method andsystem for exposing an exposure pattern on an object by a chargedparticle beam, comprising the steps of:

shaping a charged particle beam into a plurality of charged particlebeam elements in response to first bitmap data indicative of an exposurepattern, such that said plurality of charged particle beam elements areselectively turned off in response to said first bitmap data;

focusing said charged particle beam elements upon a surface of anobject; and

scanning said surface of said object by said charged particle beamelements;

said step of shaping including the steps of:

expanding pattern data of said exposure pattern into second bitmap datehaving a resolution of n times (n≧2) as large as, and m times (m≧1) aslarge as, a corresponding resolution of said first bitmap data,respectively in X- and Y-directions;

dividing said second bitmap data into cells each having a size of 2nbits in said X-direction and 2m bits in said Y-direction; and

creating said first bitmap data from said second bitmap data byselecting four data bits from each of said cells, such that a selectionof said data bits is made in each of said cells with a regularity insaid X- and Y-directions and such that the number of rows in saidX-direction and the number of columns in said Y-direction are both equalto 3 or more.

According to the present invention, it becomes possible to achieve afine adjustment of the exposure pattern by using the first bitmap datawithout considering the effect of pattern width or conducting aprocessing along the contour of the pattern boundary. Thereby, theprocessing speed and hence the exposure throughput increasessubstantially.

Another object of the present invention is to provide a BAA exposuresystem having a BAA mask wherein the deflection of the electron beamelements is made in the same direction throughout the BAA mask.

Another object of the present invention is to provide a BAA exposuresystem having a BAA mask wherein the resistance and capacitance ofwiring used for carrying drive signals to the electrostatic deflectorsprovided on the BAA mask, are optimized with respect to the timing ofturning on and turning off the apertures of the BAA mask.

Another object of the present invention is to provide a charged particlebeam exposure system for exposing a pattern on an object, comprising

beam source means for producing a charged particle beam;

beam shaping means for shaping said charged particle beam to produce aplurality of charged particle beam elements in accordance with exposuredata indicative of a dot pattern to be exposed on said object;

focusing means for focusing said charged particle beam elements upon asurface of said object; and

deflection means for deflecting said charged particle beam elements oversaid surface of said object;

said beam shaping means comprising:

a substrate formed with a plurality of apertures for shaping saidcharged particle beam into said plurality of charged particle beamelements;

a plurality of common electrodes provided on said substrate respectivelyin correspondence to said plurality of apertures, each of said pluralityof common electrodes being provided in a first side of a correspondingaperture; and

a plurality of blanking electrodes provided on said substraterespectively in correspondence to said plurality of apertures, each ofsaid plurality of blanking electrodes being provided in a second,opposite side of a corresponding aperture on said substrate.

Another object of the present invention is to provide a beam shapingmask for shaping a charged particle beam into a plurality of chargedparticle beam elements, comprising:

a substrate formed with a plurality of apertures for shaping saidcharged particle beam into said plurality of charged particle beamelements;

a plurality of common electrodes provided on said substrate respectivelyin correspondence to said plurality of apertures, each of said pluralityof common electrodes being provided in a first side of a correspondingaperture; and

a plurality of blanking electrodes provided on said substraterespectively in correspondence to said plurality of apertures, each ofsaid plurality of blanking electrodes being provided in a second,opposite side of a corresponding aperture on said substrate.

Another object of the present invention is to provide a process forfabricating a beam shaping mask for shaping a charged particle beam intoa plurality of charged particle beam elements, comprising the steps of:

providing a plurality of conductor patterns on a surface of a substratewith respective thicknesses such that at least one of said conductorpatterns has a thickness that is different from the thickness of anotherconductor pattern; and

providing a ground electrode and a blanking electrode on said substraterespectively in electrical contact with said conductor patterns, saidground electrode and said blanking electrode forming a deflector fordeflecting said charged particle beam elements.

According to the present embodiment set forth above, the beam shapingmask causes a uniform deflection when turning off the charged particlebeam, over entire area of the mask, and the problem of leakage of thedeflected charged particle beam elements upon the reversal deflectionupon the blanking of the charged particle beam is successfullyeliminated. Further, by optimizing the thickness and hence theresistance of the conductor patterns on the beam shaping meek, it ispossible to adjust the timing of activation of the individualelectrostatic deflectors formed on the beam shaping means forselectively turning off the charged particle beam elements.

Another object of the present invention is to provide a BAA exposuresystem in which maintenance of the BAA mask is substantiallyfacilitated.

Another object of the present invention is to provide a charged particlebeam exposure system for exposing a pattern on an object by a chargedparticle beam, comprising:

beam source means for producing a charged particle beam, said beamsource means emitting said charged particle beam toward an object onwhich a pattern is to be exposed, along an optical axis;

beam shaping means for shaping said charged particle beam to produce aplurality of charged particle beam elements in accordance with exposuredata indicative of a dot pattern to be exposed on said object;

focusing means for focusing said charged particle beam elements upon asurface of said object; and

deflection means for deflecting said charged particle beam elements oversaid surface of said object;

said beam shaping means comprising:

a beam shaping mask carrying thereon a plurality of apertures forproducing a charged particle beam element by shaping said chargedparticle beam and a plurality of deflectors each provided incorrespondence to one of said plurality of apertures, said beam shapingmeans further including a plurality of electrode pads each connected toa corresponding deflector on said beam shaping means;

a mask holder provided on a body of said charged particle beam exposuresystem for holding said beam shaping mask detachably thereon, said maskholder comprising: a stationary part fixed upon said body of saidcharged particle beam exposure system; a movable part provided movablyupon said stationary part such that said movable part moves in a firstdirection generally parallel to said optical axis and further in asecond direction generally perpendicular to said optical axis, saidmovable part carrying said beam shaping mask detachably; a drivemechanism for moving said movable part in said first and seconddirections; and

a contact structure provided on said body of said charged particle beamexposure system for contacting with said electrode pads on said beamshaping mask, said contact structure including a base body and aplurality of electrode pins extending from said base, said of saidelectrode pins having a first end connected to said base body of saidcontact structure and a second, free end adapted for engagement withsaid electrode pads on said beam shaping mask.

According to the construction of the present embodiment, particularlythe construction of the beam shaping mask held on the mask holder andthe construction of the cooperating contact structure, it is possible todismount the BAA mask easily, without breaking the vacuum inside theelectron beam column. Thus, the time needed for maintenance of the BAAmask is substantially reduced, and the throughput of exposure increasessubstantially. Further, the BAA exposure system of the presentembodiment is advantageous in the point that one can use various beamshaping masks by simply dismounting an old mask and replacing with a newmask. Thereby, the charged particle beam exposure system of the presentinvention is not only useful in the BAA exposure system but also in theblock exposure system.

Another object of the present invention is to provide a BAA exposuresystem capable of exposing a pattern on a large diameter substratewithout increasing the size of the control system excessively.

Another object of the present invention is to provide a charged particlebeam exposure system for exposing a pattern on an object, comprising:

a base body for accommodating an object to be exposed;

a plurality of electron optical systems provided commonly on said basebody, each of said electron optical systems including:

beam source means for producing a charged particle beam, said beamsource means emitting said charged particle beam toward an object onwhich a pattern is to be exposed, along an optical axis;

beam shaping means for shaping said charged particle beam to produce aplurality of charged particle beam elements in accordance with exposuredata indicative of a dot pattern to be exposed on said object, said beamshaping means comprising a beam shaping mask carrying thereon aplurality of apertures for producing a charged particle beam element byshaping said charged particle beam;

focusing means for focusing said charged particle beam elements upon asurface of said object;

deflection means for deflecting said charged particle beam elements oversaid surface of said object; and

a column for accommodating said beam source means, said beam shapingmeans, said focusing means, and said deflection means;

said electron optical system thereby exposing said charged particle beamelement upon said object held in said base body;

exposure control system supplied with exposure data indicative of apattern to be exposed on said object and expanding said exposure datainto dot pattern data corresponding to a dot pattern to be exposed onsaid object, said exposure control system being provided commonly tosaid plurality of electron optical systems and including memory meansfor holding said dot pattern data;

said exposure control system supplying said dot pattern data to each ofsaid plurality of electron optical systems simultaneously, such thatsaid pattern is exposed on said object by said plurality of electronoptical systems simultaneously.

According to the foregoing embodiment of the present invention, the sizeof the BAA exposure system is substantially reduced, even when exposinga large diameter wafer by using a plurality of electron optical systemssimultaneously.

Another object of the present invention is to provide a charged particlebeam exposure system that uses an immersion electron lens, wherein thecompensation of beam offset caused by the eddy current is successfullyachieved with a simple construction of the electron optical system.

Another object of the present invention is to provide a charged particlebeam exposure system for exposing a pattern on an object by a chargedparticle beam, comprising:

a stage for holding an object movably;

beam source means for producing a charged particle beam and emittingsaid charged particle beam toward said object held on said stage alongan optical axis; and

a lens system for focusing said charged particle beam upon said objectheld on said stage;

said lens system including an immersion lens system comprising: a firstelectron lens disposed at a first side of said object closer to saidbeam source means, a second electron lens disposed at a second, oppositeside of said object, said first and second electron lenses creatingtogether an axially distributed magnetic field penetrating through saidobject from said first side to said second side; and a shield plate of amagnetically permeable conductive material disposed between said objectand said first electron lens, said shield plate having a circularcentral opening in correspondence to said optical axis of said chargedparticle beam.

According to the present embodiment as set forth above, the electricfield inducted as a result of the eddy current is successfully capturedby the magnetic shield plate and guided therealong while avoiding theregion in which the electron beam passes through. Thereby, adversaryeffects upon the electron beam by the eddy current is effectivelyeliminated.

Another object of the present invention is to provide a charged beamexposure process capable of exposing both a BAA exposure process and ablock exposure process on a common substrate.

Another object of the present invention is to provide a charged particlebeam exposure system for exposing a pattern on an object, comprising:

a stage for holding an object thereon;

beam source means for producing a charged particle beam such that saidcharged particle beam is emitted toward said object on said stage alonga predetermined optical axis;

a blanking aperture array provided in the vicinity of said optical axisfor shaping an electron beam incident thereto, said blanking aperturearray including a mask substrate, a plurality of apertures of identicalsize and shape disposed in rows and columns on said mask substrate and aplurality of deflectors each provided in correspondence to an apertureon said mask substrate;

a block mask provided in the vicinity of said optical axis, said blockmask carrying thereon a plurality of beam shaping apertures of differentshapes for shaping an electron beam incident thereto;

selection means for selectively deflecting said electron beam from saidbeam source means to one of said blanking aperture array and said blockmask;

focusing means for focusing an electron beam shaped by any of saidblanking aperture array and said block mask upon said object on saidstage.

According to the construction of the present embodiment set forth above,it is possible to switch the BAA exposure and block exposure by usingthe single electron exposure system. Thereby, the addressing deflector,used in the block exposure process for selecting an aperture on theblock mask, is used also as the selection beams for selecting the BAAexposure process and the block exposure process. Thereby, no extraneousfixture is needed for implementing the selection of the exposure mode.

Other objects and further features of the present invention will becomeapparent from the following detailed description when read inconjunction with the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the scanning employed in a BAA exposuresystem;

FIG. 2 is a diagram showing a part of FIG. 1 in an enlarged scale;

FIG. 3 is a diagram showing the overall construction of a conventionalBAA exposure system;

FIG. 4 is a diagram showing an example of a BAA mask used in theexposure system of FIG. 3;

FIG. 5 is a diagram showing another example of the BAA mask;

FIG. 6 is a block diagram showing the construction of the BAA exposuresystem according to a first embodiment of the present invention;

FIG. 7 is a block diagram showing a part of the circuit of FIG. 6;

FIGS. 8A-8G are diagrams showing the timing chart for explanation of theoperation of the BAA exposure system of the first embodiment;

FIGS. 9A-9C show another timing charts for explaining the operation ofthe BAA exposure system of the first embodiment;

FIG. 10 is a diagram showing the construction of a clock generator usedin a conventional BAA exposure system of FIG. 3;

FIGS. 11A-11E are diagrams showing the clocks used in the conventionalBAA exposure system of FIG. 3;

FIGS. 12A and 12B are diagrams showing the deflector output of theconventional BAA exposure system of FIG. 3:

FIG. 13 is a block diagram showing the overall construction of the BAAexposure system according to a second embodiment of the presentinvention;

FIG. 14 is a block diagram showing the construction of a clock generatorused in the BAA exposure system of FIG. 13;

FIGS. 15A-15E are diagrams showing various clocks including the exposureclock and correction clock used in the BAA exposure system of FIG. 13;

FIG. 16 is a diagram showing the deflector output of the BAA exposuresystem of FIG. 13;

FIG. 17 is a diagram showing the overall construction of the BAAexposure system according to a third embodiment of the presentinvention;

FIG. 18 is a diagram showing the construction of a D/A converter used inthe BAA exposure system of FIG. 17;

FIG. 19 is a diagram showing the principle of the third embodiment;

FIG. 20 is a block diagram showing the process of setting voltage offsetin the BAA exposure system of FIG. 17;

FIG. 21 is a diagram showing the relationship the detected current andthe offset voltage used in the BAA exposure system of FIG. 17;

FIGS. 22A-22E are diagrams showing the operation of the BAA exposuresystem of FIG. 17;

FIG. 23 is a diagram showing the construction of a D/A converter used inthe BAA exposure system of FIG. 17;

FIG. 24 is a block diagram showing the construction of a BAA exposuresystem according to a fourth embodiment of the present invention;

FIG. 25 is a block diagram showing the construction of a BAA mask usedin the BAA exposure system of FIG. 24 together with a BAA controlcircuit cooperating with the BAA mask;

FIG. 26 is a block diagram showing the construction of the BAA controlcircuit of FIG. 25 in detail;

FIG. 27 is a block diagram showing the construction of a read/writecontrol circuit in the circuit of FIG. 25;

FIG. 28 is a diagram showing the scanning scheme used in the BAAexposure system of FIG. 24;

FIGS. 29A and 29B are diagrams showing the main deflection and stagemovement employed in the BAA exposure system of FIG. 24 as a function oftime;

FIG. 30 is a diagram showing an example of a pattern to be exposed on asubstrate in the BAA exposure system of FIG. 24;

FIG. 31 is a diagram showing the construction of a BAA control circuitused in a first modification of the fourth embodiment of the presentinvention;

FIGS. 32A and 32B are diagrams respectively showing the construction ofa BAA control circuit and exposure dot data used in the BAA exposuresystem of FIG. 24 as a second modification of the fourth embodiment;

FIG. 33 is a block diagram showing a part of the BAA control circuitused in the BAA exposure system of FIG. 24 as a third modification ofthe fourth embodiment;

FIG. 34 is a diagram showing another example of the scanning of thesubstrate by an electron beam used in the fourth embodiment of thepresent invention;

FIG. 35 is a map showing the relationship between a bit data acquisitionpoint and a corresponding beam spot point according to a fifthembodiment of the present invention;

FIG. 36 is a map showing a part of FIG. 35 in an enlarged scale;

FIGS. 37A-37D are diagrams showing the relationship between the movementof a pattern boundary and the bit data acquisition points;

FIG. 38 is a block diagram showing the construction of the circuit usedfor implementing the fifth embodiment of the present invention;

FIGS. 39A-39C are diagrams showing the construction and principle of thecircuit of FIG. 38;

FIG. 40 is a map showing the relationship between a bit data acquisitionpoint and a corresponding beam spot point according to a firstmodification of the fifth embodiment;

FIGS. 41A and 41B are diagrams showing the relationship between amovement of a pattern boundary and the bit data acquisition point in acluster of FIG. 40 according to the first modification;

FIGS. 42A and 42B are diagrams showing other examples of therelationship between a movement of a pattern boundary and the bit dataacquisition point in a cluster of FIG. 40;

FIGS. 43A, 44A, 45A and 43B, 44B, 45B are diagrams showing variousexamples of modification of the rectangular pattern data andcorresponding rectangular exposure patterns;

FIGS. 46A, 47A, 48A and 46B, 47B, 48B are diagrams showing variousexamples of modification of the triangular pattern data andcorresponding triangular exposure patterns;

FIGS. 49A-49C are diagrams showing the construction and principle of thecircuit of FIG. 38 according to the first modification of the fifthembodiment;

FIG. 50 is a map showing the relationship between a bit data acquisitionpoint and a corresponding beam spot point according to a secondmodification of the fifth embodiment;

FIGS. 51A and 51B are diagrams showing the relationship between amovement of a pattern boundary and the bit data acquisition point in acluster of FIG. 50 according to the first modification;

FIGS. 52A and 52B are diagrams showing other examples of therelationship between a movement of a pattern boundary and the bit dataacquisition point in a cluster of FIG. 50;

FIG. 53 is a diagram showing the construction of a BAA mask and aproblem thereof addressed in a sixth embodiment of the presentinvention;

FIG. 54 is a diagram showing the problem caused in a BAA exposure systemwhen the BAA mask of FIG. 53 is used;

FIG. 55 is a diagram showing the principle of a sixth embodiment of thepresent invention;

FIG. 56 is a diagram showing the construction of the BAA mask of thesixth embodiment of the present invention in a cross sectional view;

FIG. 57 is a diagram showing the construction of a BAA mask of FIG. 56;

FIGS. 58A-58C are diagrams showing the measurement of the patternresistance on the BAA mask;

FIGS. 59A and 59B are diagrams showing the construction of wiringpatterns provided on the BAA mask of the present embodiment;

FIGS. 60A-60H are diagrams showing the fabrication process of the BAAmask of the sixth embodiment;

FIGS. 61A-61D are diagrams showing the fabrication process of theconductor patterns on the BAA mask of the sixth embodiment withoptimization of the pattern thickness;

FIGS. 62A-62C are diagrams showing the process for changing thethickness of the conductor pattern partially;

FIGS. 63A-63C are diagrams showing other processes for forming theconductor patterns with respective different thicknesses;

FIG. 64 is a diagram showing the construction of a BAA exposure systemthat uses the BAA mask of the sixth embodiment;

FIG. 65 is a diagram showing a conventional construction for detachablymounting a BAA mask on a BAA exposure system;

FIG. 66 is a diagram showing the overall construction of the BAAexposure system according to a seventh embodiment of the presentinvention;

FIGS. 67 and 68 are diagrams showing the detachable mounting of the BAAmask employed in the BAA exposure system of FIG. 66;

FIGS. 69-72 are diagrams showing the construction of a mask holdermechanism for holding the BAA mask movably and detachably in the BAAexposure system of FIG. 66;

FIG. 73 is a diagram showing an example of the BAA mask used in the BAAexposure system of FIG. 66;

FIG. 74 is an example of a beam shaping mask that can be used in theexposure system of FIG. 66;

FIGS. 75A-75D show various patterns that can be exposed on a substrateby using the mask of FIG. 74;

FIG. 76 is a diagram showing another beam shaping mask;

FIG. 77 is a diagram showing the construction of a charged particle beamexposure system that uses the beam shaping mask of FIG. 76 as amodification of the seventh embodiment;

FIG. 78 is a diagram showing the construction of a beam blanking unitused in the charged particle beam exposure system of FIG. 77;

FIG. 79 is a diagram showing the deflection of the charged particle beamcaused by the beam blanking unit of FIG. 78;

FIG. 80 is a diagram showing a conventional BAA exposure system forexposing a large diameter wafer;

FIG. 81 is a diagram showing the overall construction of the BAAexposure system according to an eighth embodiment of the presentinvention;

FIG. 82 is a diagram showing a part of the BAA exposure system indetail;

FIG. 83 is a diagram showing the BAA exposure system of FIG. 81 in moredetail;

FIG. 84 is a diagram showing the adjustment employed in the BAA exposuresystem of FIG. 81;

FIG. 85 is a diagram showing the correction of the position of theelectron optical system associated with the adjustment of FIG. 84;

FIG. 86 is a diagram showing the construction of an immersion lens andthe problem occurring in an electron beam exposure system associatedwith the use of such an immersion lens;

FIG. 87 is a diagram showing the construction used conventionally foreliminating the problem of beam offset in the electron beam exposuresystem that uses an immersion lens;

FIG. 88 is a diagram showing the problem occurring in the conventionalsystem of FIG. 87;

FIG. 89 is a diagram showing an electron beam exposure system accordingto an eighth embodiment of the present invention;

FIG. 90 is a diagram showing the essential part of the electron beamexposure system of FIG. 89;

FIG. 91 is a diagram showing the axial distribution of the electricfield strength of the immersion lens system of FIG. 90;

FIG. 92 is a diagram explaining the function of a shield plate used inthe immersion lens system of the present embodiment;

FIG. 93 is another diagram explaining the function of the magneticshield plate;

FIG. 94 is a diagram showing the lateral distribution of the electricfield strength of the immersion lens system of FIG. 90;

FIG. 95 is a diagram showing the reflection of electrons occurrent inthe electron beam exposure system of FIG. 90;

FIG. 96 is a diagram showing the determination of optimum size of theshield plate of the present embodiment;

FIGS. 97A and 97B are diagrams showing the optimization of the openingprovided in the shield plate of the present embodiment;

FIG. 98 is a diagram showing the principle of a tenth embodiment of thepresent invention;

FIG. 99 is a diagram showing the overall construction of the electronbeam exposure system of the tenth embodiment;

FIG. 100 is a diagram showing the essential part of the electron beamexposure system of FIG. 99;

FIG. 101 is a diagram showing the construction of the beam shaping maskused in the electron beam exposure system of FIG. 99;

FIG. 102 is a diagram showing the construction of the exposurecontroller used in the electron beam exposure system of FIG. 99;

FIGS. 103A-103C are diagrams showing the scanning of the substrate bythe electron beam;

FIGS. 104A and 104B are diagrams showing an example of exposing asub-field;

FIG. 105 is a flowchart showing the operation of the electron beamexposure system of FIG. 99; and

FIGS. 106A-106C are diagrams showing various modifications of theexposure sequence of the electron beam exposure system of FIG. 99.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[first embodiment]

Hereinafter, the scanning of electron beam employed conventionally aswell as in a first embodiment of the present embodiment, will bedescribed with reference to FIG. 1, wherein FIG. 1 shows a scanning of asingle wafer 10 by means of electron beams forming together an electronbeam bundle. The wafer 10 corresponds to the foregoing object andincludes a plurality of regions corresponding to the chips to be formed.It should be noted, however, that the scanning scheme of the BAAexposure system is not limited to the one described in FIG. 1 but otherscanning schemes are also possible. Some of the embodiments of thepresent invention described later uses a different scanning scheme.

Referring to FIG. 1, the wafer 10 is moved continuously in a Y-directionwhile exposing the surface of the wafer 10 by electron beams shaped by aBAA mask and forming an electron beam bundle.

In such an exposure process, the scanning of the electron beam bundle tobe described is achieved in each cell defined on the wafer 10, whereinan example of such a cell is shown in FIG. 1 by a reference numeral 14.In the illustrated example, the cell 14 has a size of 2 mm in theX-direction that corresponds to the coverage area of a main deflectorused in the electron beam exposure system. On the other hand, the cell14 has a size smaller than the chip area 12 in the Y-direction. Thereby,the electron beam bundle formed of the plurality of electron beams isdeflected in the Y-direction to scan the surface of the wafer 10 whilethe wafer 10 is transported continuously in the Y-direction. Further,the scanning of the electron beam bundle is repeated while deflectingthe same in the X-direction.

As the stage carrying the wafer 10 moves in the Y-directioncontinuously, it is not necessary, in principle, to limit the size ofthe cell 14 in the Y-direction. However, it is desired to suitably limitthe size of the cell in the Y-direction in view of necessity of variousprocessings for beam compensation as well as other necessary dataprocessings of the exposure data. Typically, the size of the cell in theY-direction is set equal to the chip size in the maximum. When it isdesired to carry out more accurate beam compensation, on the other hand,one may reduce the cell size in the Y-direction.

Here, the concept of cell stripe will be defined. A cell stripe is aregion of the substrate 10 that can be exposed by a maximum deflectionof the electron beams by a sub-deflector of the electron beam exposuresystem. Typically, the sub-deflector is formed of an electrostaticdeflector and can cover an area of about 100 μm. In the case thesub-deflector can cover the area of about 100 μm by way of beamdeflection, the cell stripe has a size of 100 μm in the Y-direction.Further, when the width of the electron beam bundle in the X-directionis set to 10 μm, the cell stripe has a size of 10 μm in the X-direction.

FIG. 2 shows the black-painted region of FIG. 1 in an enlarged scale.

Referring to FIG. 2, it will be noted that there are formed a number ofcell stripes 16 each extending in the Y-direction and repeated a numberof times in the X-direction, wherein the electron beam bundle isdeflected in each cell stripe 16 in the Y-direction by the sub-deflectorsuch that the substrate is scanned by the electron beams forming theelectron beam bundle. In the case each of the cell stripes 16 has a sizeof 10 μm in the X-direction and 100 μm in the Y-direction, a regionincluding ten cell stripes 16 disposed in parallel may be scanned by thesub-deflector without energizing the main deflector or moving the stage.Thereby, the sub-deflector scans the area having a size of 10 μm×100 μm,and it should be noted that a plurality of such sub-deflector areas formthe cell region 14. As already noted, the cell region 14 has a size ofabout 2 mm in the X-direction in correspondence to the coverage area ofthe main deflector.

The cell stripe 16 may have a size smaller than the foregoing size of 10μm×100 μm. Such a reduction in the cell stripe 16 is achieved easily byturning off the electron beams from the edge region of the BAA mask. Inorder to reduce the size of the cell stripe in the Y-direction, one mayreduce the stroke of scanning in the Y-direction or turn off the beamsfrom the part of the BAA mask corresponding to the edge part of the cellstripe. It is advantageous to set the length of the cell stripecoincident to the pitch of repetition for the exposure pattern when theexposure pattern includes a repetition.

Next, the general construction of a conventional electron beam exposuresystem used for the BAA exposure will be described with reference toFIG. 3 together with problems thereof.

Referring to FIG. 3, the electron beam exposure system comprisesgenerally an electron optical system 100 that produces a focusedelectron beam and a control system 200 for controlling the electronoptical system 100. The electron optical system 100 includes an electrongun 101 as an electron beam source, and the electron gun 101 emits theelectron beam as a divergent electron beam along a predetermined opticalaxis O.

The electron beam thus produced by the electron gun 101 is shaped by anaperture 102a provided on an aperture plate 102, wherein the aperture102a shapes the electron beam upon passage therethrough. The aperture102a is in alignment with the optical axis O, and shapes the incidentelectron beam to have a rectangular cross section.

The shaped electron beam thus formed is focused on a BAA mask 110 by anelectron lens 103, wherein the BAA mask carries thereon a blankingaperture array. Thus, the electron lens 103 projects the image of theaforementioned rectangular aperture 102a on the BAA mask 110. On themask 110, there are formed a plurality of small apertures correspondingto the exposure dots to be exposed on a semiconductor substrate, and anelectrostatic deflector is provided on the BAA mask 110 incorrespondence to each of the apertures. The electrostatic deflector iscontrolled by a driving signal E to pass the electron beam directly in anon-activated state, or to deflect the passing electron beam in anactivated state, so that the direction of the passing electron beamdeviates from the optical axis O. As a result, and as will be describedbelow, an exposure dot pattern corresponding to the non-activatedapertures on the BAA mask 110 is formed on the semiconductor substrate.

The electron beam passed through the BAA mask 110 is focuses at a focalpoint f₁ on the optical axis O after passing through the electron lenses104 and 105 that form a demagnifying optical system, and the image ofthe selected apertures is projected at the focal point f₁. The focusedelectron beam is further focused on a semiconductor substrate 115 heldon a movable stage 114 by electron lenses 106 and 107 that form anotherdemagnifying optical system, after passing through a round aperture 113aprovided on a blanking plate 113. Thus, an image of the BAA mask 110 isprojected on the substrate 115. Here, the electron lens 107 acts as anobjective lens and includes therein various correction coils 108 and 109for correcting focal point and aberrations as well as deflectors 111 and112 for moving the focused electron beam over the surface of thesubstrate 115.

Further, there is provided an electrostatic deflector 116 between thelens 104 and lens 105, wherein the path of the electron beam is deviatedfrom the optical axis O, which is set to pass through the round aperture113a on the plate 113, upon activation of the electrostatic deflector116. As a result, it becomes possible to switch the electron beam on/offat a high speed on the semiconductor substrate 115. Furthermore, theelectron beams, which have been deflected by the electrostaticdeflectors on the apertures on the BAA mask 110 described above, deviatealso from the round aperture 113a. Therefore, the electron beams thusdeflected do not reach the semiconductor substrate and it becomespossible to control the exposure dot pattern on the substrate 115.

The electron-beam exposure system of FIG. 3 uses a control system 200for controlling such exposure operations. The control system 200includes an external storage device 201, such as a magnetic disk driveor a magnetic tape drive for storing data relating to the patterns ofthe semiconductor device to be exposed.

The data stored in the storage device 201 is read out by a CPU 202, andthe data compression thereof is removed by a data expansion unit 203.Thereby, the data is converted to the exposure dot data which switchesthe individual apertures on the BAA mask 110 on/off according to thedesired exposure pattern. In order to enable a delicate correction ofthe exposure pattern, the electron-beam exposure system of FIG. 3carries out a multiple exposure of exposure dots on the substrate 115,wherein N independent exposure patterns are superposed. Accordingly, thedata expansion unit 203 includes N circuits 203₁ to 203_(N), wherein thecircuits 203₁ to 203_(N) generate N sets of mutually independentexposure dot pattern data used for carrying out the foregoing multipleexposures superposed N times, based upon the exposure data provided fromthe external storage 201.

Each of the circuits 203₁ to 203_(N) is composed of a buffer memory 203afor holding exposure data supplied from the external storage 201, a dataexpansion section 203b which generates the dot pattern data representingthe exposure dot pattern based upon the exposure data held in the buffermemory 203a, and a canvas memory 203c for holding the dot pattern dataexpanded by the data expansion section 203b, wherein the data expansionunit 203 supplies the dot pattern data held in the canvas memory 203c toa corresponding shoot memory 204. More specifically, the output shootmemory 204 includes N memory circuits 204₁ -204_(N) corresponding to theN data expansion circuits 203₁ to 203_(N), and each of the memorycircuits, e.g., the circuit 204₁, includes 128 memory circuits eachformed of a dynamic random access memory, in correspondence to the totalof 128 apertures aligned in the X-direction on the BAA mask 110. Thus,each of the 128 memory circuits is supplied with one-bit data thatswitches the aperture on the BAA mask 110 on/off, from said canvasmemory 203c. The memory circuits 204₁ to 204_(N) , in turn, supply theone-bit data held therein to the BAA mask 110 after converting the sameinto analog signals by means of corresponding D/A converters 205₁ to205_(N). As a result, the electrostatic deflectors aligned in theY-direction on said BAA mask 110 in correspondence to the apertures areactivated sequentially.

Furthermore, the electron-beam exposure system of FIG. 3 includes anexposure control unit 206 which is supplied with a control signal fromthe CPU 202 based upon the control program stored in the externalstorage device 201, wherein the exposure control unit 206 controls theoperation of the data expansion circuit 203 and the shoot memory 204,the transfer of data from the data expansion circuit 203 to the shootmemory 204, and the activation of the BAA mask 110 by means of the D/Aconverter 205. Furthermore, the exposure control unit 206 controls themain deflector 111 and the sub-deflector 112 via a main deflectorcontrol circuit 207 and a sub-deflector control circuit 208, such thatthe electron beam scene over the surface of the substrate 115.

The system of FIG. 3 further includes correction circuits 207a and 208afor compensation of beam distortion respectively caused by the maindeflector and the sub-deflector, wherein the correction circuit 208a issupplied with correction coefficients GX and GY for gain, RX and RY forpattern rotation, OX and OY for pattern offset and HX and HY fortrapezoidal pattern deformation, from a deflection correction memory211, wherein the memory 211 stores the foregoing correction coefficientsat respective addresses that correspond to the main deflection datasupplied from the main deflector control circuit 207. Thus, in responseto the main deflection data from the main deflector control circuit 207,the memory 211 supplies the foregoing correction coefficients GX and GY,RX and RY, OX end OY and HX and HY to the correction circuit 208a forcorrection of the sub-deflection data supplied from the sub-deflectorcontrol circuit 208. The sub-deflection data thus corrected is thensupplied to the sub-deflector 112. Similarly, the memory 211 storescorrection coefficients DX and DY for pattern distortion at respectiveaddresses corresponding to the main deflection data and supplies thesame to the correction circuit 207 a in response to the main deflectiondata from the main deflector control circuit 207. Thereby, deflectiondata supplied from the main deflector control circuit 207 to thecorrection circuit 207a is corrected, and the deflection data thuscorrected is supplied further to the main deflector 111.

Further, the memory 211 stores correction data SX and SY for dynamicastigmatic correction as well as correction data F for dynamic focusingcorrection at respective addresses corresponding to the main deflectordata. Thereby, the dynamic astigmatic compensation is in response to themain deflection data achieved by way of the correction circuit 208asimilarly as before. Further, the dynamic focusing control is achievedin response to the main deflection data by the memory 211 that drivesthe compensation coil 108.

The electron beam exposure system of FIG. 3 further includes a refocuscontrol circuit 203e and a refocus data memory 203f for compensating forthe divergence of electron beam caused by the Coulomb repulsion ofelectrons forming the focused electron beam. The refocus control circuit203e thereby produces a drive signal of a refocus compensation coil 118in response to the exposure pattern.

Next, the construction of the BAA mask 110 will be described briefly.

Referring to FIG. 4 showing a part of the BAA mask 110 in a plan view,the BAA mask 110 is formed of a thin silicon substrate or metal plateand carries a number of apertures 120 arranged in rows and columns,wherein each of the apertures 120 includes a drive electrode 121 and aground electrode 122 at respective, mutually opposing edges of theaperture. In the illustrated example, eight of such apertures 120 arealigned in the Y-direction to form a column, and such aperture columnsextending in the Y-direction are repeated 128 times in the X-direction.As a result, there are formed eight aperture rows A-H each extending inthe X-direction, wherein each aperture row in fact is formed of twoaperture rows. For example, the aperture row A is formed of an aperturerow A₁ and an aperture row A₂, the aperture row B is formed of anaperture row B₁ and an aperture row B₂, . . . Thereby, it will be notedthat there is formed a pattern of apertures arranged in a row and columnformation in a staggered relationship on the BAA mask 110. In all, 1024apertures are formed on the BAA mask 110, each in fact including twoapertures.

Upon illumination of the BAA mask 110 of FIG. 4 by an electron beamproduced by the electron gun 101 and shaped by the aperture 102a, itwill be noted that a bundle of electron beam including a row and columnformation of electron beam elements is produced as a result of beamshaping at the apertures on the BAA mask 110. The electron beam elementsthus produced are then focused upon the substrate 115 afterdemagnification by the electron lenses 104 and 105 as well as theelectron lenses 106 and 107, and an exposure dot pattern including 1024exposure dots in maximum, each having a size of 0.08 μm×0.08 μm, isexposed on the substrate 115. In such an exposure, all the exposure dotson the substrate 115 are exposed simultaneously.

It should be noted that the electron beam elements forming the electronbeam bundle scans the surface of the substrate 115 in the Y-direction asa result of energization of the deflector 112, and each point on thesubstrate 115 experiences a multiple exposure of the exposure dots incorrespondence to the foregoing apertures forming the aperture rows A-H,wherein such a multiple exposure is repeated eight times in the maximum.

More specifically, a row of exposure dots corresponding to the aperturerow A1 are exposed on the substrate 115, followed by an exposure of theexposure dote corresponding to the aperture row B1, such that theexposure dots corresponding to the aperture row B1 are superposed uponthe exposure dots corresponding to the aperture row A1. Further, theexposure dots corresponding to the aperture rows C1, D1, . . . aresuperposed thereon. A similar situation holds also in the exposure ofdots by using the aperture rows A2, B2, C2, . . . As the apertures inthe row A1 and the apertures in the row A2 are formed with a staggeredrelationship as already noted, the exposure dots formed by the aperturerows A2 fill the gap between the exposure dots formed by the aperturerows A1, and there is formed a single exposure line extending in theX-direction as a result of such a multiple exposure of the exposuredots. By forming the apertures on the BAA mask with a staggeredrelationship as indicated in FIG. 4, it is possible to reduce theCoulomb repulsion between the electron beam elements by avoidingexcessive approaching of the electron beam elements. When such a Coulombrepulsion occurs in the electron beam elements, the effective focallength of the electron lens increases.

In the simplest case of exposure, the same exposure data is suppliedconsecutively from the aperture row A1 to the aperture rows B1, C1, D1,E1, F1, G1 and H1, or from the aperture row A2 to the aperture rows B2,C2, D2, E2, F2, G2 and H2, and there occurs a multiple exposure of theexposure dots with a desired dose. Further, it should be noted that itis possible to achieve an extremely delicate control of the exposurepattern by changing the exposure data in each aperture group such as agroup K1, K2, K3 and K4, wherein, in the illustrated example, theaperture group K1 includes the aperture rows A and B, the aperture groupK2 includes the aperture rows C and D, the aperture group K3 includesthe aperture rows E and F, and the aperture group K4 includes theaperture rows G and H. As a result of such a multiple exposure process,it should be noted that different patterns are superposed. Such amultiple exposure process is extremely useful for compensating for theproximity effect that is an unwanted exposure caused by the electronsbackscattered from the substrate. By using the foregoing multipleexposure process, it is possible to compensate for the proximity effectefficiently by a single scanning of the electron beam bundle.

FIG. 5 shows another conventional example of the BAA mask 110, whereinit will be noted that the apertures forming the groups K1-K4 are formedwith a positional offset with respect to the apertures of other groups.For example, the aperture a of the group K1 is offset with respect tothe corresponding aperture c of the group K2 in the X-direction with aquarter of the pitch of the apertures on the BAA mask 110. Similarly,the aperture a' of the group K3 is offset with respect to thecorresponding aperture a of the group K1 in the Y direction by a quarterpitch. Generally, by providing the apertures on the BAA mask 110 with amutual offset of M/N pitch (M<N) in one or both of the X- andY-directions, it is possible to achieve the desired modification of theexposure pattern with increased precision. More detailed description ofthe M/N pitch shift of the BAA mask is given in the U.S. Pat. No.5,369,282, which is incorporated herein as reference.

In such a conventional BAA exposure system, it will be noted that thedata transfer rate of the dot pattern data to the BAA exposure system isa critical factor, wherein such a data transfer of the dot pattern dataincludes decompression or expansion of pattern data in the dataexpansion unit 203b to form dot pattern data and storage of the dotpattern data thus expanded in the canvas memory 203c. In order toachieve a fast data transfer, conventional BAA exposure system has touse a very large memory for the shoot memories 204₁ -204_(N), while itis difficult, at least at the present juncture, to have a shoot memorythat can store the dot pattern data of whole chip or several chips.

Thus, in the conventional BAA exposure system, it has been practiced tointerrupt the exposure after exposing the dot pattern data held in thecanvas memory 203c for carrying out a data expansion of next patterndata. After the data expansion of the next pattern data, the exposure isresumed based upon the newly expanded data in the canvas memory 203c. Inorder to facilitate the exposure process, it is also practiced to carryout exposure while expanding the pattern data in the data expansion unit203b.

It should be noted, however, that the exposure throughput is limited insuch a conventional exposure process by the capacity of the shoot memory204 and the rate of data expansion in the unit 203b. Further, such aconventional exposure process that overwrites the exposure data in thecanvas memory by the next data, is disadvantageous in the point that itis not possible to inspect the exposure dot data in the event thereoccurred anomaly or defect in the result of exposure. Further, currentlyavailable dynamic random access memories suitable for canvas memory arevolatile in nature and cannot save the expanded dot pattern for repeateduse.

In addition, the conventional BAA exposure system has a drawback in thatthe throughput for exposing a whole area on the substrate 115 decreasessubstantially as compared with the conventional variable-shaped beamexposure process, unless the transfer of the dot pattern to the exposuresystem is achieved at very high speed.

In the BAA exposure system described above, it should further be notedthat the aperture b in FIG. 4 is separated from the aperture a in theY-direction by a distance corresponding to six apertures. Thus, theaperture b is given with the exposure data identical to the datasupplied to the aperture a with a delay of six clocks. In such aconstruction, the number of channels for supplying the dot pattern datato each of the apertures aligned on the BAA mask 110 in the Y-directionis reduced to one half as compared with the case of supplyingindependent exposure dot data to the apertures a and b. Further,independent activation of the aperture groups K1-K4 increases the numberof channels by four. Similarly, respective dot pattern data are suppliedto the aperture e, which is separated on the BAA mask 110 from theaperture a in the Y-direction by a distance of three apertures, with adelay of three clocks. Thereby, the timing of exposure has to be setextremely stringently in order to achieve exact alignment of theexposure dot formed by the aperture a and the exposure dot formed by theaperture e on the BAA mask 110.

Conventionally, such a stringent timing control of the dot pattern datahas been achieved in each channel by controlling the timing of readingthe data based upon the predicted delay of the channel, while such atiming control, requiring a precision of within several nanoseconds, hasbeen extremely difficult. It is also proposed to provide an offset tothe exposure data so as to compensate for the delay caused in the dotpattern data, while such a modification of the original exposure datahas to be changed depending upon the exposed pattern and such a processincreases the complexity of preparing the exposure pattern.

Thus, the present embodiment has an object to provide a charged particleexposure system and method for exposing versatile patterns on an objectby means of a charged particle beam that forms an exposure dot pattern,in which the creation of dot pattern data representing the exposure dotpattern and the exposure of the object by means of the charged particlebeam can be achieved separately.

Further, the present embodiment provides a charged-particle-beamexposure method and system that is capable of holding a large amount ofdot pattern data representing the exposure dot pattern and that cancontrol a blanking aperture array based upon the dot pattern data at ahigh speed for producing a charged particle beam bundle including anumber of charged particle beams in correspondence to each dot of theexposure dot pattern.

Hereinafter, the construction of the BAA exposure system according to afirst embodiment of the present invention will be described.

FIG. 6 is a block diagram showing a part of the charged particle beamexposure system according to a first embodiment of the presentinvention.

Referring to FIG. 6, there is provided a hard disk device 301corresponding to the external storage device 201 of FIG. 3 for storingpattern data to be exposed. The pattern data in the hard disk device 301is read out therefrom under control of a central controller 302corresponding to the CPU 202, wherein the exposure data thus read out isstored in a buffer memory 303 corresponding to the buffer memory 203a ofFIG. 2. The exposure data in the buffer memory 303 is then transferredunder control of a data transfer controller 304 to a data expansion unit305 corresponding to the expansion unit 203b and a canvas memory 203c,wherein the exposure data is expanded in the expansion unit 305 tobitmap data or dot pattern data that represents the exposure pattern onthe substrate 115 in the form of exposure dots. Hereinafter, theexpansion unit 305 will be referred to as a canvas memory.

The dot pattern data thus obtained in the canvas memory 305 is thensupplied, by means of a data transfer unit 306, to a number of hard diskdrives 309a-309j under control of the foregoing transfer control circuit304, wherein the transfer of the dot pattern data is achieved viatransfer channels 307a-307j and transfer controllers 308a-308jrespectively cooperating with the hard disk drives 309a-309j.

In the exposure system that uses the BAA mask 110 of FIG. 4, whichincludes 1024 apertures (=128×8), it should be noted that one has toprovide 512 channels (=1024÷2) for driving the BAA mask 110 when thesame dot pattern data is supplied to the aperture a and further to theaperture b with a delay of six clocks for the aperture b. In the eventthe accuracy of exposure is negotiable, one may supply the dot patterndata of the aperture a of the group K1 to the corresponding aperture cof the group K2 after a delay of three exposure clocks, further to thecorresponding aperture of the group K3 after a delay of additional threeclocks, and further to the corresponding aperture of the group K4 aftera delay of additional three clocks. In this case, one can reduce theindependent channels to 256 (=1024÷4).

When exposing an eight-inch wafer with a throughput of 20 wafers perhour, it is necessary to expose one wafer with a duration of 180seconds. Defining a frame on the wafer as a stripe region having a widthof 2 mm and extending in the Y-direction for a length covered by themovement of the stage 114 as indicated in FIG. 1, exposure of ten suchframes is required in order to complete the exposure of one chip havinga size of 20 mm for each edge. In each chip, the frame forms a limitedstrip or single chip fame" having a limited size of 2×20 mm, whileexposure of such a single chip frame requires exposure dot data of 25Gbits, assuming that four channels are used in the exposure

As there are 10 chip frames in one chip, it is necessary to transfer thedot pattern data for one chip frame in 18 seconds for achieving theforegoing exposure of a single chip, while this means that a datatransfer rate of 174 Mbyte/sec (=25 Gbit/18 sec) is required fortransferring the exposure dot data to the BAA exposure system. Here, itshould be noted that the same exposure dot data is used in the BAAexposure system for exposing the same chips on the wafer. Such a datatransfer rate is achieved by arranging 10 hard disk drives 309a-309jeach having a data transfer rate of 20 Mbyte/sec in parallel, such thatthe data transfer occurs in parallel in these hard disk drives.

As there are 512 independent channels for the apertures on the BAA mask110, each of the hard disk drives 309a-309j store dot pattern data forabout 52 channels.

Meanwhile, it should be noted that the exposure control system of FIG. 6achieves a refocus control such that the amount of refocus compensationincreases with increasing number of the apertures that are turned on theBAA mask 110, in order to avoid the divergence of the electron beams asa result of the Coulomb interaction of the electrons in the beams. Inorder to achieve such a refocus control, the canvas memory 305 createsrefocus data when expanding the dot pattern data, based upon the numberof bits forming the dot pattern data, wherein such refocus data istransferred from the data transfer unit 306 to another separate harddisk drive 312 via a transfer channel 320 and a transfer control circuit312. Thereby, the hard disk drive 322 constitutes the refocus datamemory 203f.

It should be noted that the foregoing dot data pattern is expanded andtransferred to the hard disk drives 309a-309j for each of the cellstripes shown in FIG. 2. In such a data transfer of the refocus data,the number of the turned-on apertures in an exposure cycle is evaluated,and the refocus data is produced for each cell region 14 called also"band," based upon the same The refocus data thus produced is thentransferred to the disk drive 312. Thereby, the disk drives 309a-309jand the disk drive 312 store the dot pattern data for one chip as wellas the refocus data.

In the construction of FIG. 6, each of the disk drives such as the diskdrive 309a cooperates with a number of high speed shoot memories such as310A_(1a), 310B_(1a), . . . 310A_(52a), 310B_(52a), wherein the shootmemories 310A correspond to the shoot memory 204 of FIG. 3. There are inall 104 such shoot memories (=52 channels×2) connected to each of thedisk drives via the foregoing transfer controller such as the controller308a. Each of the shoot memories 310 may be formed of a high speedbitmap memory such as a dynamic random access memory. Thereby, it shouldbe noted that the shoot memories are arranged to form memory pairs suchthat the memories 310A_(1a) and 310B_(1a) form a pair, . . . thememories 310A_(52a) and 310B_(52a) form a pair, wherein the memoriesforming a memory pair such as the memories 310A_(1a) and 310B_(1a) areconnected to a corresponding selector such as a selector 311_(1a).Thereby, the selector 311_(1a) selects the output of one of thecooperating memories 310A_(1a) and 310A_(1b) and transfers the same to acorresponding parallel-to-serial converter 312_(ij). A similarconstruction exists also for other hard disk drives such as the harddisk drive 309j or 322. Thereby, it will be noted that the hard diskdrives 309a-309j are disposed between the canvas memory 305corresponding to the canvas memory 203c and the shoot memories310A_(1a), 310B_(1a) -310A_(52j), 310B_(52j). Further, there areprovided also high speed shoot memories 323A and 323B cooperating withthe hard disk drive 322 for storing the refocus data transferred theretovia the transfer controller 321, wherein the memories 323A and 323B forma part of the refocus data memory 203f. The memories 323A and 323B arethereby connected to an output circuit 325 via a selector 324.

In order to control the foregoing various elements, there is provided anexposure controller 330 corresponding to the exposure controller 206 ofFIG. 3, wherein the exposure controller 330 controls the data transferof the dot pattern data for one chip frame from all of the hard diskdrives 308a-308i to the respective memory pairs by way of a transfercontroller 322, such that the dot pattern data is stored, in each memorypair, in one of the memories such as the memories 310A_(1j) -310A_(52j)or the memories 310B_(1j) -310B_(52j). Further, the exposure controller330 controls the transfer controller 332 such that the refocus data inthe hard disk drive 322 is transferred to one of the memories 323A and323B that holds the refocus data.

In order to guarantee the synchronization of data transfer, each of thetransfer controllers 308a-308j and 321 issues a completion signalindicative of completion of data transfer to the exposure controller 330via the transfer controller 332, such that any delay in data transfercaused for example by defects in the hard disk medium is compensatedfor.

Upon reception of the completion signal, the exposure controller 330carries out reading of the dot pattern data as well as the refocus datafrom the memories 310A_(1j) -310A_(52j) or from the memories 310B_(1j)-310B_(52j), wherein the transfer controller 332 reads out the dotpattern data, under control of the exposure controller 330, from thememories 310A_(1a) -310A_(52a) or from the memories 310B_(1a)-310B_(52a) substantially simultaneously and transfers the same to theparallel-to-serial converters 312_(1a) - 312_(52a), . . . 312_(1j)-312_(52j). Further, the refocus data is read out from one of thememories 323A and 323B and is transferred to the output circuit 325 viathe selector 324.

After the foregoing data transfer is completed, the exposure controller330 activates a similar data transfer from the other memories such asthe memories 310B_(1a) -310B_(52a), . . . 310B_(1j) -310B_(52j) as wellas from the other memory 323B, assuming that the data transfer has beenmade in the previous step from the memories 310A_(1a) -310A_(52a), . . .310A_(1j) -310A_(52j) and from the other memory 323A.

It will be noted that the system of FIG. 6 further includes a SEM/MDcontroller 335, while this controller 335 is used for controlling theSEM operation or marker detection of the electron beam exposure system.As the controller 335 is outside the scope of the present invention,further description thereof will be omitted.

According to the exposure system of FIG. 6, it will be noted that theexpansion of the dot pattern data can be achieved separately to theexposure operation. This in turn means that the throughput of exposureis not influenced by the rate of the data expansion. By using suchpre-expanded dot pattern data stored in the hard disk drives, it ispossible to expose the pattern of integrated circuits repeatedly on ormore wafers by merely reading out the dot pattern data from the harddisk drives. As such hard disk drives are not volatile in nature, it ispossible to examine the dot pattern data held in the hard disk drive inthe event there occurred an anomaly in the exposed pattern for anydefects. As the actual exposure is achieved by transferring the dotpattern data from each of the hard disk drives to a number of high speedmemories cooperating with each of the hard disk drives in parallel, itis possible to read out and transfer the dot pattern data from such highspeed memories, and a high exposure throughput can be attained as aresult. As the reading of the dot pattern data is achieved from thememories 310A_(1a) -310B_(52j) in synchronization under control of anexposure clock, the exposure dots are formed on the substrate 115 withexact alignment. One may use high speed volatile memories such as adynamic random access memory or static random access memory for thememories 310A_(1a) -310B_(52j) as well as for the memories 323A or 323B.

In the construction of FIG. 6, it should be noted that the exposurecontroller 330 controls the transfer of the dot pattern data such thatthe reading of the dot pattern data is carried out from the first memoryset that includes the memories 310A_(1a), . . . 310A_(52a), . . .310A_(1j), . . . 310A_(52j), while simultaneously writing the dotpattern data into the second memory set that includes the memories310B_(1a), . . . 310B_(52a), . . 310B_(1j), . . . 310B_(52j), or viceversa. Thereby, it is possible to eliminate the interruption of theexposure that may occur while rewriting the memories by next dot patterndata or refocus data.

FIG. 7 shows the construction of the parallel-to-serial converter suchas the converter 312_(1a) in a block diagram.

Referring to FIG. 7, the parallel dot pattern data of 64 bits read outform a corresponding high speed memory such as the memory 310A_(1a) andis supplied, via a corresponding selector such as the selector 311_(1a),to a parallel-to-serial conversion unit 350 that includes a register.Thereby, the register holds the parallel dot pattern data suppliedthereto and outputs the same as serial dot pattern data with a clockspeed of 400 MHz.

The serial dot pattern data thus obtained is then supplied from theconversion unit 350 to an inversion switching circuit 352 for causing aselective data inversion, wherein the inversion switching circuit 352supplies the serial dot pattern data to a delay circuit 353 that causesa delay in the serial data supplied thereto, with an inversion in thepolarity of the serial dot data in response to a control signal from thecentral controller 302. By providing the inversion switching circuit352, it is possible to select the positive exposure and negativeexposure of the exposure dot on the substrate 150 simply under controlof the central controller 302, while such a negative/positive control ofthe exposure dot pattern is extremely effective for compensating for theproximity effect.

The serial dot pattern data thus delayed in the delay circuit 353 isthen supplied to next delay circuits 354 and 355 in parallel fordelaying, therein the serial dot pattern data thus delayed in thecircuits 354 and 355 are supplied further to phase correction circuits356 and 357, respectively for timing correction. Thereby, the serial dotpattern that has experienced timing correction in the phase correctioncircuit 356 is supplied to the drive electrode 121 on the BAA mask 110via a selector 358 and the D/A converter 205 described in FIG. 3,wherein the selector 358 selects either the serial dot pattern data orthe SEM/MD data in response to a SEM/MD control signal supplied from thecontrol circuit 335. Similarly, the serial dot pattern processed by thephase correction circuit 357 is supplied to the BAA mask 110 afterpassing through a selector 359 similar to the selector 358 and after aD/A conversion in the D/A converter 205.

Here it should be noted that the delay circuit 353 provides a delay tothe serial dot pattern data based upon a control signal from the centralcontroller 302, wherein the amount of delay of the delay circuit 353 ischanged with respect to the delay of other channels. For example, thedelay circuit 353 of a parallel-to-serial conversion circuit 312 that isincluded in one of the circuits 312_(1a) -312_(52j) and controls theapertures a and b on the BAA mask 110 of FIG. 4 or FIG. 5, provides adelay of three clocks to the serial dot pattern data, wherein the delaycircuits 354 and 355 provide respectively a zero clock delay and 6 clockdelay. Similarly, the parallel-to-serial conversion circuit 312 for theapertures c and d causes a delay of 12 clocks. Here, the clocks have afrequency of 400 MHz and are used as the data transfer clock as will bedescribed below. In each of the parallel-to-serial conversion circuits312, it should be noted that the delay circuits 354 and 355 are set, bythe central controller 302, to have a predetermined delay correspondenceto the distance between the apertures exposed consecutively by the samedot pattern data. For example, the delay circuit 355 for the aperture bprovides a delay of 6 clocks with respect to the delay circuit 354 incorrespondence to the separation from the aperture a of 6 clocks.

As a result of the setting of the delay as set forth above, the dotpattern data shown in FIG. 8B is supplied to the aperture m insynchronization to the data transfer clock of FIG. 3A. Further, the samedot pattern data as the one shown in FIG. 8B is supplied to the apertureb after a delay of 6 clocks as indicated in FIG. 8C. Further, the nextdot pattern data different from the one shown in FIG. 8B is supplied tothe aperture e as indicated in FIG. 8D with a delay of three clocks fromthe data of FIG. 8B, and the same dot pattern data as indicated in FIG.8D is supplied to the aperture f as indicated in FIG. 8E with a delay of6 clocks. Similarly, the next dot pattern data different from any of theforegoing dot pattern data is supplied to the aperture c with a delay of12 clocks with respect to the data of FIG. 8B as indicated in FIG. 8F,and the same dot pattern data as the data of FIG. 8F is supplied to theaperture d with a delay of 6 clocks from the data of FIG. 8F, asindicated in FIG. 8G.

It should be noted that the phase correction circuits 356 and 357 areused to correct the timing of the data and provides a minute delay tothe serial dot pattern data supplied thereto under control of thecentral controller 302, wherein the timing correction is made with adivision of 1/10 the interval of the data transfer clock shown in FIG.8A.

In the exposure system described above, the delay of the dot patterndata is made in each of the channels. Thus, there is no need to adjustthe timing of the dot pattern data when transferring the dot patterndata, and the control of the data transfer to the BAA mask issubstantially simplified. Thereby, it should be noted that the relativetiming between the channels is determined by the delay circuit 353 whilethe relative timing within the channel is determined by the delaycircuits 354 and 355. As the timing of the dot pattern data is furtheradjusted by means of the phase correction circuits 356 and 357, it ispossible to align the exposed dote exactly on the substrate 115.

As already noted, the selectors 358 and 389 are supplied with one bitdata indicative of the SEM/MD data as well as a selection control signalfrom the SEM/MD controller 335. Thus, the selectors 358 and 359selectively outputs the SEM/MD data in response to the selection controlsignal when operating the electron beam exposure system in the SEM/MDmode, while in the normal exposure mode, the selectors 358 and 359selectively supply the serial dot pattern data from the phase correctioncircuits 356 and 357 to the BAA mask 110.

It should be noted that the output circuit 325 of FIG. 6 supplies therefocus data supplied thereto via the selector 324 to the electron lens109 in synchronization to the dot data from the output circuits 312_(1a)-312_(52a), . . . , 312_(1j) -312_(52j) for controlling the intensity ofthe electron lens 109.

Next, the operation of the exposure controller 330 will be describedwith reference to FIGS. 9A-9C.

Referring to FIG. 9A, the exposure controller 330 reads the dot patternA shown in FIG. 9B from a memory such as the memory 310A_(1a), . . . byissuing a read control signal CW1 shown in FIG. 9A and transfers the dotpattern data A thus read out to the parallel-to-serial conversion unit350 of a corresponding parallel-to-serial converter such as 312_(1a) byissuing a transfer control signal CR₁ shown in FIG. 9C. Similarly, thedot pattern data B shown in FIG. 9B is subsequently read out from adifferent memory such as the memory 310B_(1a) in response to the readcontrol signal CW₂ shown in FIG. 9A, wherein the exposure controller 330causes a transfer of the data B thus read out to the parallel-to-serialconversion unit 350 of the corresponding parallel-to-serial converter byissuing a transfer control signal CR₂.

In the event the same dot pattern data B is used repeatedly in theexposure, it should be noted that the exposure controller 330 issues thetransfer control signals CR₂ -CR₄ without issuing the read controlsignal. Thereby, the same dot pattern data held in the memory 310B_(2a),. . . are repeatedly transferred to the corresponding parallel-to-serialconverts 312_(1a), . . . As the same dot pattern data is used for such arepetitive exposure of dot patterns already held in the memories 310A or310B, it should be noted the step for expanding the data in the harddisk drive such as the hard disk 309a for each exposure can be omitted.Here, the memories 310A and 310B includes the foregoing memories310A_(1a) -310A_(52j) and 310B_(1a) -310B_(52j).

[second embodiment]

Next, a second embodiment of the present invention will be described.

In the conventional electron beam exposure systems that carry outvariable beam shaping or block exposure, an example of which isdescribed in the U.S. Pat. Nos. 5,173,582 or 5,194,741, the exposure anddeflection of the electron beam are generally conducted repeatedly andalternately.

More specifically, the electron beam is deflected to a desired positionon the substrate prior to the exposure or "shot," and variouscorrections such as beam position correction, focusing correction,aberration correction, and the like, are carried out for exposing asharply defined pattern on the substrate. It should be noted that thecalculation of such a correction has to be completed during thedeflection process conducted before the electron beam is actuallyirradiated upon the substrate, wherein such a deflection process of theelectron beam includes the setting of beam trajectory and cancellationof beam blanking, in addition to the energization of the deflectors.Once the deflection of the electron beam is thus completed, actualexposure of the electron beam is conducted for a suitable duration,which is determined by the current density and the sensitivity of theelectron beam resist on the substrate.

It should be noted that such an exposure is controlled in response tothe exposure clock. In other words, the exposure clock is set so as toprovide a desired exposure duration based upon the current density andthe resist sensitivity. The exposure clock is generally produced bydividing a system clock with an optimum divisional ratio with respect tothe current density and the resist sensitivity, while the same exposureclock is used also for driving the aberration correction systems orrefocusing systems. It should be noted that the correction coils anddeflectors are activated only when the exposure of a pattern is made onthe wafer.

FIG. 10 shows the block diagram of a conventional clock generator.

Referring to FIG. 10, a system clock, an example of which is shown inFIG. 11, is produced by a system clock generator 400 wherein the systemclock thus produced is supplied to a frequency divider 401. Thefrequency divider 401, in turn, is supplied further with a controlsignal specifying the frequency divisional radio, which is determinedbased upon the current density of the electron beams and the sensitivityof the electron beam resist, and carries out a frequency-division of theforegoing system clock to produce various clocks such as the exposureclock, the correction clock, refocusing clock, and the like. Forexample, FIG. 11B shows the exposure clock obtained by dividing thesystem clock of FIG. 11A by four, while FIG. 11D shows a correctionclock corresponding to the exposure clock of FIG. 11B. Similarly, FIG.11C shows the exposure clock obtained by dividing the system clock ofFIG. 11A by two, while FIG. 11E shows a correction clock correspondingto the exposure clock of FIG. 11C.

In the BAA exposure system of FIG. 3, on the other hand, the exposureand the deflection of the electron beam are conducted simultaneously. Insuch an exposure process, a high frequency is used for the exposureclock when each of the electron beam elements has a high current densityor when a high sensitivity electron beam resist is used for reducing thedose. On the other hand, the frequency of the exposure clock is reducedwhen the current density of the electron beam element is low or theelectron beam resist has a low sensitivity for increasing the dose.

When the exposure clock is changed in the conventional BAA exposuresystem in correspondence to the current density of the electron beam orthe sensitivity of the electron beam resist, it will be noted that thecorrection clocks for the calculation of the beam position correction,focusing correction, aberration correction, and the like, have to bechanged also. Associated therewith, there arises problems as will beexplained below.

FIG. 12A shows a digital output of a deflection control circuitcorresponding to the sub-deflector control circuit 208 of FIG. 3, forthe case wherein a high speed exposure clock of 400 MHz is used togetherwith a beam correction calculated in response to a correction clock ofthe same frequency. In this case, it will be noted that the digitaloutput of the deflection control circuit, which uses the deflection datasubjected to the correction, changes with a substantial rate, and a D/Aconversion unit cooperating with the deflection control circuit producesa generally linear analog output as indicated by a broken line. Inresponse to the analog output thus produced, the electron beam isdeflected and scans the surface of the substrate.

When the exposure clock is reduced to 200 MHz, on the other hand, thedigital output of the deflection control circuit changes with muchreduced rate as indicated in FIG. 12B, and the analog output of thecooperating D/A converter shows a conspicuous saturation as indicated bya broken line in FIG. 12B. With such a saturation in the analog outputof the deflection control circuit, the analog output of the deflectioncontrol circuit does not reach the predetermined level and the electronbeam can no longer hit the intended point on the substrate.

Accordingly, the object of the present embodiment is to provide acharged particle beam exposure system and method wherein a highprecision exposure is guaranteed even when the setting for the currentdensity of the electron beam or the sensitivity of the electron beamresist is changed.

More specifically, the present invention provides a method for exposinga pattern on an object by means of a charged particle beam, comprisingthe steps of:

shaping a charged particle beam into a plurality of charged particlebeam elements forming collectively a charged particle beam bundle havinga desired pattern in response to exposure data;

calculating a focusing error correction and an aberration correction tobe applied upon said charged particle beam elements when exposing saiddesired pattern on said object, as a function of said exposure data,said step of calculation being conducted in response to a correctionclock; and

exposing said desired pattern upon said object by radiating said chargedparticle beam bundle upon said object;

said step of exposing comprising the steps of:

setting an exposure clock speed based upon a sensitivity of an electronbeam resist provided on said object and a current density of saidcharged particle beam elements; and

emitting said charged particle beam elements forming said chargedparticle beam bundle upon said object in response to said exposureclock, with said focusing error correction and said aberrationcorrection;

wherein said correction clock is held in the vicinity of a predeterminedclock speed when changing a clock speed of said exposure clock in saidstep of setting the exposure clock speed.

Further, the present invention provides a charged particle beam exposuresystem for exposing a desired pattern on an object, comprising:

a charged particle beam source for producing a charged particle beam andemitting the same along a predetermined optical axis;

beam shaping means provided on said optical axis so as to interrupt saidcharged particle beam, said beam shaping means carrying thereon aplurality of apertures for shaping said charged particle beam into aplurality of charged particle beam elements collectively forming acharged particle bundle, each of said apertures carrying switching meansfor selectively turning off said charged particle beam element inresponse to exposure data;

beam focusing means for focusing each of said charged particle beamelements forming said charged particle beam bundle upon said object;

deflection means for deflecting said charged particle beam elementscollectively over a surface of said object in response to a deflectioncontrol signal supplied thereto;

deflection control means supplied with deflection data for producingsaid deflection control signals;

beam correction means for calculating a correction to be applied to saidelectron beam element as a function of said exposure data, said beamcorrection calculation means carrying out the calculation in response toa correction clocks;

exposure control means for conducting an exposure of said chargedparticle elements in response to an exposure clock; and

clock control means supplied with control data indicative of a currentdensity of said charged particle beam elements and a sensitivity of saidelectron beam resist, for producing said exposure clock and saidcorrection clock, such that said exposure clock has a clock speeddetermined as a function of said control data, said clock control meansfurther holding said correction clock substantially constantirrespective of said exposure clock.

According to the invention of the present embodiment, one can guaranteea necessary exposure dose by changing the exposure clock as a functionof the resist sensitivity and the current density. On the other hand,the analog signal supplied to the deflection means, which includes amain deflector and a sub-deflector, changes generally linearly withtime, and the problem of the exposure beam failing to hit the desiredpoint on the substrate is effectively eliminated.

FIG. 13 shows the construction of the electron beam exposure systemaccording to the present embodiment, wherein those parts correspondingto the parts described already are designated by the same referencenumerals and the description thereof will be omitted.

Referring to FIG. 13, it will be noted that the exposure controller 206includes a clock generator 206a, wherein the exposure controller 206controls the clock generator 206a in response to the exposure conditionsuch as the current density on the substrate 115 or the resistsensitivity from the CPU 206.

FIG. 14 shows the construction of the clock generator 206a.

Referring to FIG. 14, the clock generator 206a includes a clockoscillator 501 and a frequency divider 502, wherein the clock oscillator501 produces a system clock in the range of 400-500 MHz as an exposureclock in response to a control signal supplied from the exposurecontroller 206. Further, the clock oscillator 301 supplies the systemclock thus produced to the foregoing frequency divider 502 as well asselectors 503₁ and 503₂.

It should be noted that the frequency divider 502 is formed of a counter503₁ as well as counters 502₂ -502_(i), wherein each of the counters502₂ -502_(i) cooperates with an AND gate. Thereby, the counters 502₁-502_(i) divides the frequency of the system clock with variousdivisional ratios such as 1/2, 1/3, 1/4, . . . and produces clocks ofrespective frequencies, wherein the counter 502₁ divides the systemclock with a ratio of 1/2, 1/4, 1/8, 1/16, 1/32, . . . , while thecounter 502₂ cooperating with an AND gate divides the system clock witha ratio of 1/3. Similarly, the counter 502₃ cooperating with an AND gatedivides the system clock with a ratio of 1/5, and so on.

The clocks thus produced as a result of the division of the system clockare supplied to the selector 503₁ as well as to the selector 503₂,wherein each of the selectors 503₁ and 503₂ is supplied with a controlsignal from the exposure controller 206. Thereby, the selector 501₁selects one of the clocks supplied thereto such that the selected clockhas a frequency of about 10 MHz. Thus, the selector 501₁ selects a clockdivided by a ratio of 1/40 when the frequency of 400±5 MHz, while theselector 501₁ selects a clock divided by a ratio of 1/39 when the systemclock has a frequency of 390±5 MHz. Similarly, when the system clock hasa frequency of 100±5 MHz, the selector 501₁ selects a clock divided by aratio of 1/10. When the system clock has a frequency of 50±5 MHz, theselector 501₁ selects a clock divided by a ratio of 1/5. In any case,the selector 501₁ produces a clock signal having a frequency ofapproximately 10 MHz, wherein the clock signal thus obtained is suppliedto the main deflector control circuit 207 and the sub-deflector controlcircuit 208 of FIG. 13 as a correction clock of substantially constantfrequency.

The selector 503₂, on the other hand, selects a clock signal of thefrequency in the range of 100-50 MHz by dividing the system clock of thefrequency of 400-200 MHz by a ratio of 1/4. When the system clock has afrequency of 200-100 MHz, the selector 503₂ selects a clock signal ofthe frequency in the range of 100-50 MHz by dividing the system clock bya ratio of 1/2. Further, when the system clock is set below 100 MHz, theselector 503₂ outputs the system clock directly, without dividing thefrequency. The output of the selector 503₂ is thereby used as a refocuscorrection clock and stored in the data memory 203f of FIG. 13.

In the construction set forth above, the correction clock maintains asubstantially constant frequency even when the system clock and hencethe exposure clock is changed in correspondence to the current densityand the resist sensitivity as indicated in FIGS. 15A and 15B, whereinFIG. 15A shows a system clock of 200 MHz while FIG. 15B shows a systemclock of 100 MHz. It should be noted that the correction clock obtainedfrom the selector 503₁ maintains a constant frequency as indicated inFIG. 15C, even when the system clock has changed from the one shown inFIG. 15A to the one shown in FIG. 15B, while the correction clockobtained from the selector 503₂ changes from the one shown in FIG. 15Dto the one shown in FIG. 15E, wherein the clock of FIG. 15D has afrequency of 100 MHz while the clock of FIG. 15E has a frequency of 50MHz. Thus, it will be noted that the selector 503₁ produces a correctionclock with a substantially constant frequency, while the selector 503₂produces a correction clock with a semi-fixed frequency.

In the exposure system of FIG. 13, the shoot memory 204 supplies theblanking data to the cooperating D/A converter 205 in response to theexposure clock. Further, the main deflector control circuit 207 and thesub-deflector control circuit 208 calculates the main deflection dataand the sub-deflection data in synchronization to the foregoingcorrection clock of 10 MHz based upon the exposure data suppliedthereto, wherein the main deflection data and the sub-deflection dataare converted to respective analog signals by corresponding D/Aconverters. As the correction clock has a fixed frequency of about 10MHz, it will be noted that the correction in the correction circuits207a and 208a is carried out with a proper timing.

As the correction clock is fixed to the frequency of approximately 10MHz irrespective of the exposure clock, it should be noted that thedigital output of the deflector control circuits changes generallylinearly as indicated in FIG. 16 by a continuous line, and thecorresponding analog output changes generally linearly as indicated inFIG. 16 by a broken line. In other words, the beam position changesgenerally linearly with time, and one can hit the desired point on thesubstrate 115 by a focused electron beam with high precision.

On the other hand, the refocus data memory 203f is supplied with therefocus clock of the foregoing semi-fixed frequency of 100 MHz and readsout the refocus control data therefrom in synchronization with therefocus clock, wherein the refocus control data thus read out is used todrive the electron lens 106. As the refocus control is conducted suchthat the amount of correction increases with the current density andhence the number of turned-on apertures on the BAA mask 110, such arefocus control, in principle, has to be conducted in synchronizationwith the exposure clock. On the other hand, increase of the refocuscorrection clock above 100 MHz does not result in the desired correctioneffect, as the electron lens 106, having a relatively slow response,cannot follow the high frequency correction clock. As the number of theturned-on apertures on the BAA mask 110 does not change substantiallywithin several periods of the exposure clock, the use of the correctionclock of 100 MHz does not cause any serious problem in the refocuscontrol. As already noted, the refocus clock, derived by the frequencydivision of the system clock and hence the exposure clock, issynchronized with the exposure clock, and is advantageously used for thedesired refocus control.

In the event the exposure clock frequency is reduced below 10 MHz, theexposure clock produced by the clock generator 501 may be supplieddirectly to the selector 501₁ in addition to the frequency-dividedclocks such that the selector 501₁ selects one of the clocks suppliedthereto including the system clock itself.

[third embodiment]

Next, a third embodiment of the present invention will be described.

In the BAA exposure system described heretofore, it will be noted thatthe electron beam produced by the electron gun 101 and shaped by theaperture 102a has to cover a substantial area on the BAA mask 110 with auniform intensity of beam radiation.

It should be noted that the BAA mask 110 is formed such that theapertures thereon have a size of 25 μm for each edge, wherein the sizeof the apertures is determined in view of the damage to the substrate ofthe BAA mask by the electron beam and the easiness for the formation ofconductor patterns thereon. Thus, a BAA mask including thereon 128×8apertures arranged in staggered row and column formation, inevitably hasa size of 3200 μm (=25 μm×128) in the column direction, while this sizeis substantially larger than the size of the aperture used in theconventional variable-shaped beam exposure systems. Thus, the BAAexposure System is required to have a capability of illuminating a widearea of the beam shaping mask or BAA mask as compared with theconventional electron beam exposure systems.

In order to achieve such a uniform illumination of the BAA mask by theelectron beam over an extended area, it is necessary to improve theelectron gun as well as the electron optical system. Further, effortshave been made to optimize the pixel size of the BAA mask.

As a result of such efforts including the improvement in the tip shapeof the electron gun, substantial improvement has been achieved withrespect to the coverage area of the electron beam over the BAA mask,while the uniformity of the beam radiation intensity is stillinsufficient. Currently, the beam intensity decreases in the marginalarea of the BAA mask by a factor of 20% as compared with the centralarea of the BAA mask. While this figure is a substantial improvement,the uniformity in the beam intensity is still insufficient as alreadynoted. Because of the poor beam intensity distribution, the exposuredots formed on the substrate in correspondence to the marginal part ofthe BAA mask tend to have a reduced size due to the insufficientexposure dose or current density, and there is a tendency that a band ofexposure dots is formed on the substrate with a width of about 10 μm incorrespondence to the foregoing size of the BAA mask demagnified by afactor of 1/300.

With the improvement of the electron optical system, it is now possibleto cover an area on the BAA mask that is four times as large as the areaconventionally covered by the electron beam, by increasing themagnification of the electron optical system that focuses the electronbeam upon the BAA mask, while this is still insufficient in view of thearea of the BAA mask that is twelve times as large as the area of theconventional beam shaping mask. While it is possible to increase themagnification further, excessive increase in the magnification raises aproblem in that the magnification of the image at the round aperture onthe blanking plate decreases inevitably and the turning on and turningoff of the electron beam at the round aperture becomes incomplete.

Even when the variation in the electron current density is suppressedwithin 10% as a result of improvement of the electron gun and theelectron optical system, the foregoing band of the exposure dots on thesubstrate persists.

In order to eliminate the foregoing problem of formation of the bands ofexposure dote on the substrate, it is also possible to change the sizeof the individual apertures on the BAA mask such that the reduction insize of the exposure dots is compensated for. Thus, the apertures on theBAA mask is formed with an increased size at the marginal area thereofas compared with the central area. However, such compensation tends tobe lost when the electron gun is replaced or the electron column issubjected to maintenance.

Accordingly, the present embodiment addresses the foregoing problems andprovides a charged particle beam exposure system and method that iscapable of exposing an object by charged particle beams produced by aBAA mask with a uniform electron beam intensity irrespective of thelocation of the apertures on the BAA mask that are used for shaping theelectron beams.

More specifically, the present embodiment provides a method for exposinga pattern on an object, comprising the steps of:

shaping a charged particle beam into a plurality of charged particlebeam elements forming collectively a charged particle beam bundle havinga desired pattern in response to exposure data;

exposing a desired pattern upon said object by radiating said chargedparticle beam bundle upon said object;

said step of beam shaping comprising the steps of:

activating a plurality of apertures provided on a beam shaping mask forshaping said charged particle beam, such that a predetermined number ofsaid apertures are activated each time as a unit, each of said aperturesincluding a deflector for deflecting a charged particle beam elementpassing therethrough in response to an activation of said aperture, saidpredetermined number of apertures thereby producing a plurality ofcharged particle beam elements equal in number to said predeterminednumber; and

detecting the intensity of said predetermined number of charged particlebeam elements on said object;

said step of activating said plurality of apertures being conducted suchthat the intensity of said charged beam elements, produced as a unit, isequal to the intensity of said charged particle beam elements of otherunits, by optimizing an energization of said deflectors on saidpredetermined number of apertures.

The present embodiment further provides a charged particle beam exposuresystem for exposing a pattern on an object, comprising:

a charged particle beam source for producing a charged particle beam andemitting the same along a predetermined optical axis;

beam shaping means provided on said optical axis so as to interrupt saidcharged particle beam, said beam shaping means carrying thereon aplurality of apertures for shaping said charged particle beam into aplurality of charged particle beam elements collectively forming acharged particle bundle;

switching means for selectively turning off said charged particle beamelement in response to a control signal;

driving means for driving said switching means on said beam shapingmeans by supplying thereto said control signal in response to exposuredata;

beam focusing means for focusing each of said charged particle beamelements forming said charged particle beam bundle upon said object;

detection means for detecting the intensity of said charged particlebeam elements on said object;

correction means for controlling said driving means such that saiddriving means supplies said control signal to said switching means withan offset added thereto, said correction means evaluating said offset inresponse to the intensity of said charged particle beam elementsdetected by said detection means, such that a group of charged particlebeam elements including a predetermined number of charged particle beamelements therein has an intensity that is substantially identical to theintensity of other charged particle beam elements forming other groups,each of said other groups including said charged particle beam elementsin number identical to said predetermined number.

According to the present invention as set forth above, the intensity ofthe charged particle beam elements is detected for each unit or groupincluding a predetermined number of charged particle beam elements,wherein the intensity of the charged particle beam elements is adjustedfor each unit in response to the detected beam intensity on the object,by adjusting the energization of the switching means or deflectorscooperating with each of the apertures, such that the beam intensity issubstantially uniform over the entire surface of the object. Thereby,the problem of the exposure dots shaped by the apertures on the marginalarea of the BAA mask is substantially eliminated, and a high precisionexposure becomes possible.

FIG. 17 shows the overall construction of the electron beam exposuresystem according to the present embodiment, wherein those partsidentically constructed to the parts described previously are designatedby the same reference numerals.

Referring to FIG. 17, it will be noted that the exposure system includesa current detector 151 for detecting the substrate current produced as aresult of irradiation of the electron beams, wherein the detector 151 isconnected to a Faraday cup 150 provided on the stage 114 and produces anoutput indicative of the electron beam current. The output of thecurrent detector 151 is supplied to the CPU 202. Further, there isprovided an offset register 250 controlled by the CPU 202, wherein theregister 250 stores offset control data provided by the CPU 202 for eachof the apertures on the BAA mask 110 in response to the output of thecurrent detector 151. Thereby, the offset register 250 controls the D/Aconverter 205 such that the analog output of the D/A converter 205 isoffset by an amount corresponding to the offset control data.

In operation, the Faraday cup 150 is aligned to the optical axis O ofthe electron optical system 100 and the apertures on the BAA mask areturned on one by one, while monitoring for the electron beam currentproduced by the electron beam captured in Faraday cup 150 by means ofthe current detector 151. Thereby, it will be noted that the electronbeam current for each aperture on the BAA mask 110 is obtained.

FIG. 18 shows the construction of a D/A converter unit included in theD/A converter 205 for driving a BAA aperture in the form of a blockdiagram.

Referring to FIG. 17, the D/A converter unit includes a variable voltagegenerator 600 to which the offset control data is supplied from theoffset register 280 typically in the form of four bit data, wherein thevoltage generator 600 selectively produces one of sixteen level offsetvoltages in response to the foregoing four bit offset control data andsupplies the offset voltage to a terminal a of a switch 601. Typically,the output voltage of the voltage generator 600 falls in the rangebetween 0-2 volts.

The switch 601 further includes a terminal b to which a constant voltageof 10 volts is supplied. Further, the switch 601 includes a controlterminal d to which the blanking data of one bit is supplied from theshoot memory 204. Thereby, the switch 601 connects the terminals a and cwhen the content of the blanking data is "1," and the output voltage ofthe variable voltage generator 600 is supplied to the aperture electrode121 on the BAA mask 110. On the other hand, the foregoing voltage of 10volts on the terminal b is supplied to the aperture electrode 121 whenthe content of the blanking data is "0." Thereby, the electron beamelement produced by the aperture is turned off.

FIG. 19 shows the shaping and focusing of the electron beam elementsproduced by the BAA mask 110.

Referring to FIG. 19, the electron beam produced by the electron gun 101is shaped by the BAA mask 110 as already described, and the electronbeam elements produced as a result of the beam shaping are focused uponthe focal point f₁ that corresponds to the blanking plate 113 thatcarries the round aperture 113a thereon. After passing through the roundaperture 113a, the electron beam elements are focused upon the substrate115 by the electron lenses 105-170 (see FIG. 17).

when the aperture electrode 121 on the BAA mask 110 is applied with thevoltage of 10 volts, the electron beam element misses the round aperture113a as indicated by an arrow I₁ and is interrupted by the blankingplate 113. Thereby, the electron beam element is turned off on thesubstrate 115.

In the case the voltage applied to the aperture electrode 121 is zero,on the other hand, the electron beam element passes straight through theround aperture 113a and reaches the surface of the substrate 115. On theother hand, when a voltage is applied to the aperture electrode 121within the magnitude of about 2 volts, the electron beam elementexperiences an offset in the direction shown by an arrow I₂, and theelectron beam element is partially interrupted by the round aperture113a. Thereby, the intensity of the electron beam element arriving atthe substrate 115 is diminished as a function of the offset voltageapplied to the aperture electrode 121.

In the construction of FIG. 19, it should further be noted that theoffset voltage is applied with a polarity such that the electron beamelement shifts in the same direction as the arrow I₁ upon theapplication of the offset voltage as indicated by the arrow I₂. As aresult, one can avoid the problem of transitional leakage of theelectron beam to the substrate 115 when switching the electron beamelement on and off.

FIG. 20 shows the flowchart for setting the amount of voltage offset tobe applied to the aperture electrode 121. It should be noted that theprocess of FIG. 20 is typically conducted after a maintenance operationsuch as a replacement of the electron gun or periodical maintenance,under control of the CPU 202.

Referring to FIG. 20, a step S10 is conducted first, wherein the stage114 is moved to a position in which the Faraday cup 150 is aligned withthe optical axis O.

Next, in the step of S20, all the apertures on the BAA mask 110 areturned on, and a step S30 is carried out wherein the electron beam pathis optimized such that the electron beam current detected by thedetector 151 becomes maximum.

Next, in the step of S40, a predetermined number of the apertures on theBAA mask 110, which may also be a single aperture, are turned on, andthe electron beam current for this state is detected in the step of S50.Further, a step S60 is conducted wherein the CPU 202 obtains an offsetvoltage for the currently turned-on aperture by referencing to a map ofFIG. 21 showing the relationship between the detection current and thevoltage offset. Further, a step S70 is conducted wherein the offsetcontrol data corresponding to the offset voltage obtained in the stepS70 is stored in a register forming a part of the register 250 andcorresponding to the foregoing aperture currently turned on.

Next, in the step S80, a discrimination is made whether the setting ofthe offset voltage is complete for all of the 8×128 apertures, whereinif the result of discrimination is NO, the process returns to the stepS40 and the steps S40-880 are repeated for the next aperture, until thesetting of the offset control data is completed for all of theapertures.

FIG. 22A shows the BAA mask 110 while FIG. 22C shows the distributionprofile of the electron beam for the aperture row A₁. As will be notedin FIG. 22C, the electron beam intensity decreases at the both endregions of the BAA mask 110 with respect to the X-direction. Associatedwith this, the detection current shows a pattern analogous to the curveshown in FIG. 22C.

FIG. 22D shows the offset voltage obtained from the map of FIG. 21,wherein the offset voltage is low (≈0 V) in the end regions of the BAAmask 110 in the X-direction and is high in the central region thereof(about 2 V). Thus, the offset control data is set for each of theapertures on the BAA mask 110 in the register 250 in accordance with theoffset voltage of FIG. 22D. Thus, by applying the offset voltage of FIG.22D to the electrodes of the apertures aligned on the BAA mask 110, onecan compensate for the variation of the beam intensity profile on thesubstrate 115 as indicated in FIG. 22E. In FIG. 22E, it will be notedthat the electron beam intensity is uniform in the X-direction.

It should be noted that a similar intensity distribution of the electronbeam intensity in the X-direction appears not only in the aperture rowA₁ but also in the aperture rows A₂, B₁, B₂, . . . Further, such adistribution profile appears also in the Y-direction as indicated inFIG. 22B.

In the present embodiment, it will be noted the one can set theintensity of the electron beam elements arriving at the surface of thesubstrate 115 substantially uniform, by compensating for the intensitydistribution profile by providing an intentional offset. Thereby, it ispossible to carry out the exposure of desired pattern with highprecision.

The process of FIG. 20 is also advantageous in the point that theelectron optical system is adjusted in the step 30 or maximizing thedetection current. This is particularly important, as the adjustment ofthe electron beam intensity is made so as to diminish the intensity ofthe strong electron beam elements by way of providing an offset on theBAA mask.

It should be noted that the present embodiment does not require anymodification of the BAA mask 110 itself and does not bring anycomplexity in the fabrication of the BAA mask. Further, one can connectthe ground electrodes 122 on the BAA mask commonly as indicated in FIG.22A.

Of course, it is possible to provide the offset voltage to the groundelectrodes 122 in the BAA mask 110 shown in FIG. 4 or FIG. 5, whereinthe ground electrodes 122 are separated from each other. In this case,however, it is necessary to invert the polarity of the offset voltagesuch that the electron beam is offset in the direction I₂ that is thesame beam deflection direction I₁ for turning off the electron beamelement.

It should be noted that the distribution of the electron beam intensityin the Y-direction shown in FIG. 22B may not be compensated for, as theexposure of the dots is made on the substrate 115 repeatedly in theY-direction. For example, a point on the substrate 115 may be exposed byan electron beam element formed by an aperture in the aperture row A₁,followed by an electron beam element formed by another aperture alignedin the Y-direction with respect to the foregoing aperture and includedin the aperture row B₂. Similarly, the exposure is repeated in theY-direction by the apertures in the aperture rows C₁ and C₂ notillustrated in FIG. 22A.

In such a multiple exposure process, it is obvious that the variation ofthe electron beam intensity in the Y-direction does not cause anysubstantial problem in the exposed dot pattern on the substrate 115, aslong as the variation in the X-direction is successfully compensatedfor. This in turn means that one may repeatedly use the offset controldata stored in the offset register 250 also for other aperture rows eachextending in the X-direction and repeated in the Y-direction.

FIG. 23 shows the construction of the D/A converter 205 in the form of ablock diagram.

Referring to FIG. 23, it will be noted that the D/A converter 205includes variable voltage generators 600₁, 600₂, . . . each suppliedwith offset control data of four bits from the offset register 250,wherein each of the variable voltage generators produces an offsetvoltage signal that changes in 16 levels in response to the four bitdata supplied thereto. Thereby, the offset voltage produced by thevariable voltage generator 600₁ is supplied to the switches 601Aa and601Ba commonly, while the offset voltage produced by the variablevoltage generator 600₂ is supplied to the switches 601Ab and 601Bacommonly.

It will be noted that the switches 601Aa, 601Ba, . . . are connected tothe drive electrode of respective apertures aligned on the BAA mask 110in the Y-direction. Similarly, the switches 601Ab, 601Bb, . . . areconnected to the drive electrode of respective apertures also aligned onthe BAA mask 110 in the Y-direction. The switches 601Aa, 601Ba, 601Ab,601Bb, . . . thereby produce an output voltage of 10 volts in responseto the blanking data when turning off the electron beam element for thepertinent aperture, similarly to the switch 301 of FIG. 18. Further, theswitches produce the offset voltage for causing the desired offset ofthe electron beam element on the aperture plate 113. Thereby, bysupplying the same offset voltage to the switches such as the switches601Aa, 601Ab, . . . aligned in the Y-direction, such that the aperturesaligned in the Y-direction are supplied with the same offset voltage, itis possible to reduce the number of the variable voltage generatorssubstantially.

In the construction of FIG. 23, it should further be noted that the sameoffset voltage may be applied to two or there apertures aligned in theX-direction, as it is expected that the offset voltage does not changesubstantially in two or three successive apertures aligned in theX-direction. Further, one may group the apertures on the BAA mask 110into a number of groups each including a plurality of apertures alignedin the X- and Y-directions and to supply the offset voltage to each ofsuch groups, such that the same offset voltage is applied to theapertures belonging to the same group.

Of course, the present embodiment may be used in combination with theconstruction of the BAA mask in which the size of the apertures ischanged in the central area and in the marginal area of the mask.

[fourth embodiment]

Next, a fourth embodiment of the present invention will be described.

In the BAA exposure system and method described heretofore, it will benoted that the exposure data held in the external storage device such asa disk drive is transferred to the bit map memory or shoot memory at ahigh speed, wherein the bit map data of the exposure pattern is read outfrom the shoot memory for exposure also at a high speed, wherein thewriting and reading of the shoot memory is conducted alternately or inparallel.

In the conventional BAA exposure system, however, the speed of datatransfer from the external storage device to the shoot memory cannot beincreased as desired and the process of data transfer is becoming abottle neck of the high throughput exposure.

Thus, the present embodiment addresses the problem of improving the datatransfer rate and hence the exposure throughput of the BAA exposuresystem by compressing the dot pattern data during the process of datatransfer.

More specifically, the present embodiment provides a method for exposinga pattern on an object by means of a charged particle beam, comprisingthe steps of:

producing a plurality of charged particle beam elements in the form ofdot pattern data, said plurality of charged particle beam elements beingproduced simultaneously as a result of shaping of a single chargedparticle beam by a mask, said mask carrying a plurality of beam shapingapertures arranged in rows and columns on a mask area;

focusing said plurality of charged particle beam elements upon anobject; and

scanning a surface of said object by means of said plurality of chargedparticle beam elements in a first direction;

said step of producing the plurality of charged particle beam elementsincludes the steps of:

dividing said dot pattern data into a plurality of data blocks eachcorresponding to a rectangular area on said beam shaping mask, saidrectangular area having a size in a second direction perpendicular tosaid first direction such that said size is smaller than a size of saidmask area in said second direction;

providing identification codes to said data blocks for discriminatingsaid data blocks from each other, such that identical data blocks havean identical identification code;

storing said data blocks respectively in corresponding dot memories,together with said discrimination codes corresponding to said datablocks;

reading out said data blocks from said dot memories consecutively byspecifying said identification codes consecutively; and

shaping said single charged particle beam by said beam shaping mask intosaid plurality of beam shaping beam elements in response to said datablocks read out from said dot memories.

Further, the present embodiment provides a charged particle beamexposure system for exposing a pattern on an object, comprising:

beam source means for producing a charged particle beam and for emittingthe same along an optical axis in the form of a charged particle beamtoward an object;

beam shaping means disposed on said optical axis so as to interrupt saidprimary charged particle beam, said beam shaping means carrying on amask area thereof a plurality of apertures each supplied with exposuredot data representing a dot pattern to be exposed on said object, saidapertures thereby shaping said charged particle beam into a plurality ofcharged particle beam elements in response to said exposure dot data,said plurality of charged particle beam elements as a whole forming acharged particle beam bundle;

focusing means for focusing each of said charged particle beam elementsin said charged particle beam bundle upon said object with ademegnification;

scanning means for scanning a surface of said object by said chargedparticle beam elements in a first direction;

a dot memory for storing dot pattern data for data blocks eachcorresponding to a group of exposure dots to be formed on a rectangulararea on said object, said rectangular area having a size on said object,in a second direction perpendicular to said first direction, to be equalto or smaller than a size of said mask area projected upon said objectand measured in said second direction;

a code memory for storing codes each specifying one of said data blocks;

block addressing means for addressing, based upon said codes read outfrom said code memory, said dot memories consecutively from a firstaddress to a last address of a data block specified by said code; and

code memory control means for reading said codes from said code memoryconsecutively in the order of exposure.

According to the present invention set forth above, the same exposuredata is used repeatedly by specifying the codes. It should be noted thatthe same data block has the same code. Thereby, the amount of the dotpattern data is substantially reduced. It should be noted that such areduction in the amount of data decreases the duration of data transfer,and the throughput of exposure is improved substantially.

FIG. 24 shows the BAA exposure system according to the presentembodiment.

Referring to FIG. 24, an electron beam EB0 produced by an electron gunis passed through a BAA mask 730 to form a plurality of electron beamelements collectively represented as an electron beam EB2. Similarly asbefore, the electron beam elements to be turned off are interrupted by ablanking plate 718 as indicated by a beam EB0 by experiencing adeflection at the BAA mask 730. Further, a substrate 710 to be exposedis held on a movable stage 712 that is moved under control of a stagecontrol circuit 714, therein the position of the stage 712 is detectedby a laser interferometer 716 that feeds back the result of detection tothe stage control circuit 714. The substrate 710 carries thereon aresist film on which the foregoing electron beam EB2 impinges afterpassing through a round aperture provided on the foregoing blankingplate 718.

The electron beam EB2 thus arrived at the substrate 710 is deflected bya magnetic main deflector 720 and an electrostatic sub-deflectordisposed above the movable stage 712 while moving the substrate 710 bydriving the movable stage 712, wherein the electron beam EB2 scans overthe surface of the substrate 710. It should be noted that the movablestage 712 provides the largest area of scanning while the speed of thescanting is smallest in the stage 712. On the other hand, thesub-deflector 722 provides the fastest scanning speed while the areathat is covered by the sub-deflector 722 is the smallest. Further, maindeflector 720 provides an intermediate scanning speed and intermediatearea of scanning.

FIG. 28 shows the scanning conducted on the surface of the substrate710, wherein it should be noted that the scanning of the presentembodiment is different from the scanning described in FIGS. 1 and 2with reference to the first embodiment.

Referring to FIG. 28, the main deflector 720 deflects the electron beamEB2 continuously in a principal scanning direction D1 while moving thestage 712 and hence the substrate 710 thereon continuously in asecondary direction D2. Further, the sub-deflector 722 is activated suchthat the electron beam EB2 follows continuously the movement of thesubstrate 710 in the direction D2. Thereby, an exposed area A0 that isthe area of the substrate 710 exposed by a single shot of the beam EB2forms a band extending in the direction D1. Typically, the band haslength of 2 mm in the elongate direction and a width of 10 μm and isscanned with a duration of 100 μs. In this case, the stage 712 is movedin the Y-direction with a speed of 100 mm/s (=10 μm/100 μs).

FIG. 29A shows movement of the electron beam EB2 on the substrate 710caused by the main deflector 720, wherein the electron beam position isdesignated by X. Further, FIG. 29B shows the position Y of the stage 712as detected by the laser interferometer 716 as well as the amount ofdeflection of the electron beam EB2 caused by the sub-deflector 722represented as Y-Y_(i).

Referring to FIG. 28, the same pattern is exposed on the chip areasC1-C11, wherein the stage 712 is moved such that the same frame such asa frame A4 is exposed repeatedly as indicated by arrows, while using thesame dot pattern data of the frame A4.

In order to achieve such a control of the exposure, the BAA exposuresystem of FIG. 24 uses a main control circuit 724 that supplies a targetstage position to the stage control circuit 714 as well as a periodicalsawtooth signal to an amplifier 726. The circuit 724 thereby receives asignal Y indicative of the current stage position from the laserinterferometer 716 and a band coordinate Yi to be described later from aBAA control circuit 740 and supplies a signal proportional to thequantity Y-Yi indicative of the sub-deflection distance, to an amplifier728. The amplifiers 726 and 728 in turn produces respective drivesignals as a result of current amplification and a voltageamplification, wherein the drive signals thus produces are supplied tothe main deflector 720 and to the sub-deflector 722.

As already noted, the BAA mask 730 is disposed above the aperture plate718 as indicated in FIG. 24, wherein the BAA mask 730 includes a numberof apertures 733 within a BAA area 732 of a thin substrate 731 with astaggered relationship. Similarly to the embodiments before, eachaperture 733 includes a common electrode 734 and a blanking electrode735 at both sides thereof, wherein the common electrode 734 is connectedto the ground commonly to the electrodes 734 of other apertures.

Thus, the BAA mask 730 shapes the electron beam EB0 supplied thereto andcovering the BAA area 732 with a generally uniform current density toform the foregoing electron beam EB2, wherein the beam EB2 passesthrough the round aperture on the aperture plate 18 and reaches thesubstrate 10 when the blanking electrode 35 of the BAA mask 30 is set tothe zero or ground voltage level. When a voltage Vs of a predeterminedlevel is applied to the blanking electrode 35, on the other hand, theelectron beam EB2 experiences a deflection and is interrupted by theblanking plate 718 as indicated by the beam EB0. Thus, it is possible toexpose a desired fine exposure pattern on the substrate 10 by applyingselectively the voltage level Vs to the electrode 735 in response to thedot pattern data of single bit.

Typically, the aperture 733 has a square shape having a size of 25 μmfor each edge, wherein the electron beam element shaped by the aperture733 exposes a square dot on the substrate 710 with a size of 0.08 μm foreach edge. In the description hereinafter, two of the aperture columnsextending in the Y-direction are treated as a single aperture column.Although the illustrated BAA mask 730 includes only 3×20 apertures, theactual BAA mask 730 includes 8×128 apertures similarly to the previousembodiments. In the description hereinafter, it is assumed that theapertures 733 are formed in m×n formation, wherein m represents thecolumn extending in the Y-direction while n represents the row extendingin the X-direction. Thereby, the aperture 733 at the column 1 and row iwill be designated as 733(i,j). Similarly, FIG. 25 shows thecorresponding electrode designated as 35(i,j).

In the construction of FIG. 25, it will be noted that the apertures 33are formed with a pitch p in the X-direction such that the area forproviding electrodes 34 and 35 as well as the corresponding conductorpattern is secured. Typically, the pitch p is set three times as largeas a length a of the aperture 733.

FIG. 30 shows a part of the conductor pattern of a random access memoryto be formed on the substrate 710 together with the size of the BAA area732.

Referring to FIG. 30, the dot pattern data of the frame A4 is dividedinto a number of block data each corresponds to the dot pattern data ofa block having a size PX in the X-direction and a size PY in theY-direction, wherein the foregoing division of the dot pattern data isadvantageously made in correspondence to the patterns that are repeatedin the frame A4. The pitch PY of the block should be taken as large aspossible but not exceeding the size PYm of the BAA region 732 in theY-direction. Further, the pitch PX is set to be an integer fraction ofthe length of the band A2 such that the exposure of the band A2 isachieved by repeating the exposure of the block a plurality of times.The block herein corresponds to a cell stripe A1 shown in FIG. 28. Inthe random access memory of the illustrated example, the cell stripe A1defined in FIG. 30 by the one-dotted-chain corresponds to a singlememory cell, wherein such a memory cell is repeated a number of times.The cell stripe defined herein differs from the previous definition ofthe cell stripe given in FIG. 1 in that the cell stripe in the presentembodiment serves as a unit of data expansion and data compression. Inother words, the data expansion and compression are conducted in thepresent invention for each cell strip such as the one defined in FIG.28.

In FIG. 30, it should be noted that the BAA area 732 is divided into thearea A0 falling inside the cell stripe A1 and regions 737 and 738outside the cell stripe A1, wherein the voltage Vs is supplied to theblanking electrodes 735 for the apertures on the BAA mask 730corresponding to the regions 737 and 738.

Next, the construction of the BAA control circuit 740 will be describedwith reference to FIG. 25.

Referring to FIG. 25, the BAA control circuit 740 includes a number ofdot memories 741j (j=1-n) in correspondence to the blanking electrode735 of the j-th row for storing single bit data, wherein the dotmemories 741j have the same storage capacity.

In cooperation with the dot memories 7411-741n, there is provided acontrol circuit 743 operating in synchronization with a clock φ0,wherein the circuit 743 controls a read/write circuit 742 that writesthe dot pattern data supplied from the main control circuit 724 into thedot memories 741j as well as reads out the dot pattern data therefrom.Each of the dot memories 7411-741n has a memory area divided into aplurality of areas, wherein one of the memory area is used for thewriting the dot pattern data by way of direct memory access processwhile the other of the memory areas is used for the reading the dotpattern data. Thereby, each time the reading and writing for one frame,the frame A4, is completed, the memory area for wiring and the memoryarea for reading are switched with each other. Further, it should benoted that the data corresponding to the areas 737 and 738 Of FIG. 30are all set to "0."

In operation, the control circuit 743 supplies the read/write controlsignals to the dot memories 7411-741n, wherein the dot pattern data readout from a shoot memory such as the memory 741j is supplied to thelowermost bit of a corresponding shift register 744j. The dot patterndata is thereby forwarded to an upper bit in response to a clock fromthe control circuit 743, wherein the clock is set to have a period Tidentical to the period of the clock used for reading the shoot memory741j. It should be noted that the shoot memory collectively designatedby 741 is a bitmap memory typically formed of a dynamic random accessmemory.

As will be apparent from FIG. 26, each of the blanking electrodes735(i,j) is supplied either with the drive voltage of the level Vs orthe ground level voltage via a switch 745 forming a buffer circuit,wherein each of the switches 745 is controlled by a data output of acorresponding shift register 744j (j=1-4) that stores the output dotpattern data of the dot memories 7411-7414, wherein the outputs of theshift registers are supplied to respective control terminals of theswitches 745.

More specifically, it should be noted that the k-th bit measured fromthe lowest, zero-th bit of the shift register 744j is supplied to theblanking electrode 735(i,j), wherein the bit k is determined as

    k=2(p/a)(i-1) when j is odd,

or

    k=(p/a)(2i-1) when j is even,

wherein the parameters p and a are defined already. Thus, only when theforegoing k-th bit of the shift register 744j stored the data "1," theground or zero voltage is applied to the corresponding blankingelectrode 735(i,j), and the aperture 733(i,j) corresponding to theblanking electrode 735(i,j) allows the passage of the electron beam.Further, the scanning speed of the electron beam in the X-direction isset such that the electron beams passed through the apertures 733(2,j),733(3,j), . . . 733(m,j) hit a common point P on the substrate 710consecutively at the respective timings of t=2(p/a)T, t=4(p/a)T, . . . ,t=2(m-1)(p/a)T, wherein the point P is the same point that has beenscanned by the electron beam passed through the aperture 733(1,j) at thetiming t=0.

By setting the scanning as such, the same point on the substrate 710experiences exposure repeatedly by the same data for m times. Further,the areas on the substrate 710 located between the points exposed at atime t by the beams passed through the apertures 733(i,j), j=1, 3, 5, .. . , n-1, are exposed by the electron beams respectively passed throughthe apertures 733(i,j), j=2, 4, 6, . . . , n, at a timing of t+(p/a)T.

Next, the construction of a read circuit 7421 included in the read/writecircuit 742 will be described with reference to FIG. 27.

Referring to FIG. 27, the read circuit 7421 includes an up/down counter750, a band memory 751, an up counter 752, a cell stripe memory 753,registers 754-56, an operational circuit 57, and an up counter 58,wherein the band memory 751 stores the Y-coordinate of the band A2 shownin FIG. 28 as well as the corresponding first address AS0. It should benoted that the first address AS0 of the cell stripe represents theaddress of the cell stripe memory 753 for the first cell stripe A1 ofthe band A2. Further, the address of the band memory 751 is specified bya count AB of the up/down counter 750.

It should be noted that the control circuit 743 supplies a load controlsignal, a clock φ1 and an up/down control signal respectively to a loadcontrol terminal L, a clock terminal CK and an up/down control terminalU/D of the up/down counter 750, wherein the up/down counter 750 isloaded with an initial value when the load control terminal L is setactive. Thereby, the initial value is given as the first address AB0 ofthe first band of the band memory 751 when the up/down counter 750 isoperating in the up-counting mode in response to the high level inputsupplied to the up/down control terminal U/D. When the up/down counter750 is operating in the down-counting mode in response to the low levelinput to the input terminal U/D, on the other hand, an address ABE ofthe last band on the band memory 751 is used for the foregoing initialvalue. It should be noted that the first address AB0 and the lastaddress ABE correspond respectively to positions B0 and Be of the frameA4 shown in FIG. 28.

When the initial value is thus loaded upon the up/down counter 750, thenumber of the bands ABN0 (=E+1) is loaded on a down counter 7431provided in the control circuit 743, wherein the count ABN of the downcounter 7431 is reduced one by one in response to each occurrence of theclock φ1. When the count ABN of the down counter 7431 has reached zero,the exposure of one frame A4 is completed.

The first address ASO of the cell stripe read out from the band memory751 is then loaded on the up counter 752 to set the initial valuethereof, in response to the load control signal from the control circuit743. Further, the address data Yi of the Y-coordinate of the band readout concurrently to the foregoing first address AS0, is supplied to themain control circuit 724 of FIG. 24. Thereby, the up-counter 752calculates the number of the clocks φ2 supplied from the control circuit743 to produce a count AS indicative of the result of the counting,wherein the count As thus obtained is used for specifying the address ofthe cell stripe memory 753.

When the initial value AS0 is loaded upon the up-counter 752, a valueASN0 indicative of the number of the cell stripes in a band is loaded ina down-counter 7431, wherein the down-counter 7431 decreases the numberof the count ASN one by one in response to each occurrence of the clockφ2. When the count ASN has reached zero, the exposure for one band A2 iscompleted. Further, simultaneously to the completion of the exposure ofthe band A2, the clock φ1 rises and the first address AS0 of the nextcell stripe is loaded upon the up-counter 752.

It should be noted that the cell stripe memory 753 stores the cellstripe numbers as the identification of the cell stripes A1. Thus, whenthe address AS0 is set 81, the count AS increases from the first addressS1 of the cell stripe to the address S2-1 one by one consecutively, andcell stripe numbers N10-N13 corresponding to the cell stripes A10-A13 ofFIG. 24 are read out from the cell stripe memory 753.

The output N of the cell stripe memory 753 is held in a register 754. Onthe other hand, the register 755 holds data A indicative of the numberof the dots of a cell stripe A1 in the X-direction, while the register756 holds a base address B. The operational circuit 757 in turncalculates the first address A·N+B and supplies the same to theup-counter 758. Thereby, the first address A·N+B is loaded upon theup-counter 758 in response to the load control signal from the controlcircuit 743. The up-counter 758 then counts the number of clocks φ3supplied from the control circuit 743 and specifies the address of theshoot memory 7411 based upon the count AD thus obtained.

When the initial value A·N+B is loaded upon the up-counter 758, dataADN0 indicative of the number of the dots of one cell stripe in theX-direction is loaded upon the down-counter 7433 in the control circuit743. Thereby, the count ADN of the down-counter 7433 is decreased one byone in response to each clock φ3. When the count ADN of the down-counter7433 has reached zero, the exposure of one cell stripe A1 is completed.

Simultaneously to the completion of the exposure of the cell stripe A1,the clock φ2 is activated, and data A·N+B indicative of the next stripeis loaded upon the up-counter 758.

It should be noted that the data of the foregoing band memory 751 andthe cell stripe memory 753 form a part of the exposure data and arestored in the external storage device similarly to the dot pattern datafor the dot memories 7411-741n and are loaded from the external storagedevice.

According to the present embodiment, one can reduce the amount ofexposure data by repeatedly using the same dot pattern data for the casewhen the same dot pattern such as the pattern for the cell stripe A1 isexposed repeatedly. In such a case, the same block is specified byspecifying the cell stripe number N. As a result, the time needed fortransferring the exposure data from the external storage device to thedot pattern memory is substantially reduced and the throughput of theexposure is improved accordingly.

Further, the present embodiment, which uses the band memory 751, isadvantageous in the point that it does not require storage of the samecell stripe numbers a number of times in the cell stripe memory 753. Itis only required to specify the first address of the cell stripe in theband A2 as long as the same exposure dot pattern is exposed. Thereby,further reduction of the exposure data is achieved.

While there occurs a case in which the direction of scanning is oppositein the first exposure and in the second exposure as in the case ofexposing the chip area C1 and the chip area C2 as indicated in FIG. 24,such a change in the scanning direction is easily attended to bychanging the up/down counting mode of the up/down counter 750 as well asthe initial value thereof.

In order to exploit the advantage of the present embodiment, it isdesired to divide the dot pattern data into the frames A4 such thatthere occurs repetition of patterns as much as possible and such thatthe pitch PY is increased as much as possible. For this purpose, it isdesired that the pitches PX and PY are variable, while it should benoted that there exists a constraint that the width of the band A2 hasto be held constant. Thus, the present embodiment achieves the desiredchange of the pitch PY while using the cell A3 as a unit, wherein thecell A3 that includes therein a plurality of bands A2. Thereby, one maydefine the cell A3 as being coincident to the frame A4. As the number ofthe dots and hence the number of the bits of one cell stripe A1 in theX-direction changes with the pitch PX of the cell stripe A1, the valueof N has to be changed appropriately such that the address spaceA·N+B-A·(N+1)+B-1 does not overlap with each other. It should be notedthat such a change of the pitch causes a change in the number of value Aof the register 755. For example, the number N is changed to N+1.Alternatively, the base address may be changed.

[first modification of the fourth embodiment]

FIG. 31 shows the construction of the BAA control circuit according to amodification of the present embodiment in detail.

It should be noted that the present modification relates to thecompensation of the proximity effect or other minute adjustment of theexposure pattern by changing the exposure dot pattern in each shot inplace of exposing the same pattern repeatedly m times.

For this purpose, the present embodiment represents the same exposurepoint on the substrate 710 by independent data of m/2 bits and uses thedata of 1 bit twice, repeatedly. As the exposure of one dot column isachieved by n apertures each using the m/2 bit data for each exposurepoint, the exposure of one column requires the data of m×n/2 bits.Further, the use of the one-bit data twice indicates that the shootmemory of m×n/2 is required for supplying the m×n/2 bit datasimultaneously to the m×n apertures 733.

Thus, the construction of FIG. 31 uses mutually independent dot memories741(i,j) for each of the odd column apertures 733(i,j) (i=1-n, j=1, 3,5, . . . , m-1). Thereby, the output of the shoot memory 741(i,j) forthe odd value of j is passed through a delay circuit 746(i,j) for adelay time of (p/a)(i-j)T. The data thus delayed is then used forcontrolling the switch element of a buffer circuit 745A such that one ofthe blanking voltage Vs and the ground voltage is supplied to theblanking electrode 734(i,j) of the BAA mask 730. Further, the same datais passed through another delay circuit 746(i+1,j) for a delay of2(p/a)T, wherein the data thus delayed is used for controlling anotherswitch element of the buffer circuit 745A such that one of the voltageVs and the ground voltage 0 is supplied to the blanking electrode735(i+1,j). In the case of i-1, the delay time (p/a)(i-1) is zero, andthus, there is no delay circuit 746(l,j).

Generally, a kT delay circuit delays the input signal supplied theretoby a delay time that is k times as large as the period T for reading thebits from the shoot memory 741(i,j), and may be formed of a k-bit shiftregister.

The output of the dot memories 741(i,j) for the even value of the suffixj is used similarly as before, except that the delay caused by the delaycircuit 746(i,j) is longer than the case of odd value of the suffix j bya duration of (p/a)T and that there exists the delay circuit 746(l,j)for i=1.

By using the delay circuit 746(i,j) as set forth above, each of the dotmemories stores the dot data of the same exposure column at the sameaddress, and the processing of the dot pattern data to be supplied tothe BAA control circuit 740 is simplified substantially.

In the event the dot pattern data is not compressed as set forth above,it will be noted that one requires the exposure dot of m/2 times ascompared with the case of the fourth embodiment of the presentinvention. In the modification of the present embodiment, a furthercompression of the exposure data becomes possible.

[second modification of the fourth embodiment]

FIG. 32A shows a part of the BAA control circuit according to a secondmodification of the present embodiment.

According to the fourth embodiment or the modification thereof, it willbe noted that the reading of the dot pattern data with a high clockspeed such as 400 MHz is possible. In such a high throughput exposureprocess, however, the speed of the memory operation may become a bottleneck.

Thus, the present modification of the fourth embodiment uses a shootmemory 741A that allows the reading of the dot pattern data for eachu-bits of the data. The output data DAT of the shoot memory 741A is thenconverted to serial data d in a parallel-to-serial converter 747 and issupplied to the shift register 744i of FIG. 25 or to the 3(i-1)T delaycircuit 746(i,j) of FIG. 31. It should be noted that theparallel-to-serial converter 747, producing one bit output in responseto a single clock, operates at a higher speed as compared with the shootmemory 741A. By setting the size u to be 20, for example, the dotpattern data is read out from the shoot memory 741A with a speed of 20MHz (=400 MHz/20).

In the event a single aperture 733 on the BAA mask 730 is used forexposing a pattern of the size of ds×ds on the substrate 710, it will benoted that the number of the bits g of the dot pattern data in theX-direction of a cell stripe having the pitch PX, is given as q=PX/ds inthe foregoing fourth embodiment. In the case of the foregoingmodification of the fourth embodiment, this value q is given as q=4PX/ds. On the other hand, when the quantity q is not an integer multipleof the quantity u, continuous exposure is no longer possible.

Thus, in order to avoid this problem, the present modification employsthe following processes.

(1) Expand the q-bit to ([q/u]+1), wherein [q/u] represents the integerpart of the quantity q/u. This expansion may be conducted by carryingout a linear interpolation. Thereby, the dot memories store the dotpattern data thus expanded.

(2) Increase the dot density on the substrate 710 by σ times, wherein σis given as σ=([q/u]+1)u/q. In order to increase the dot density in theX-direction by σ times, the ratio of (speed of reading the dot patterndata)/(electron beam scanning speed) is increased by σ times. This meansthat one may increase the speed of reading the dot pattern data σ timeswhile holding the electron beam scanning speed constant, or decrease theelectron beam scanning speed by 1/σ times while holding the speed ofreading the dot pattern data constant. In any case, the stripe memory753 of FIG. 27 stores the parameter such as 1/σ, σ or q together withthe cell stripe number, such that the speed of reading the dot patterndata or the electron beam scanning speed is changed in response to theparameters 1/σ, σ or q.

When increasing the electron beam scanning speed by 1/σ times, it isnecessary to increase the scanning speed by 1/σ times for each of themovable stage 712, the main deflector 720 and the sub-deflector 722,wherein such an increase of the scanning operation, caused insynchronization to a clock, is achieved by supplying a variable clock bymeans of a PLL circuit. It should be noted that the signals supplied tothe amplifiers 726 and 728 are converted to analog signals by a D/Aconversion after the digital processing.

[third modification of the fourth embodiment]

FIG. 33 shows a part of the BAA control circuit according to a thirdmodification of the fourth embodiment.

Referring to FIG. 33, it will be noted that the exposure dot data forthe regions 737 and 738 of the BAA area 732 are zero (0) incorrespondence to the region outside the valid exposure area. While suchdot data may be written into the dot memories, it is also possible toset the corresponding output of the dot memories forcedly to zero.

Thus, in the present modification of the fourth embodiment, there isprovided a BAA valid/invalid register 748 of n-bit length for storingthe dot pattern data for the exposure dots aligned in the Y-direction,such that the register 748 includes an invalid field corresponding tothe foregoing regions 737 and 738 and a valid field corresponding to theregion A0, wherein the data of the invalid field are all set to "0,"while the data of the valid field are all set to "1." Further, there areprovided n AND gates 7491-749n, wherein each of the AND gates such asthe AND gate 749j (j=1-n) has a first input terminal to which the i-thbit of the register 748 is supplied and a second input terminal to whichthe output of the shoot memory 741j of FIG. 25 is supplied. Thereby, theAND gate 749j supplies the output thereof to the lowermost bit of theshift register 744j of FIG. 25.

According to the present embodiment, the need for writing the invaliddata "0" to the shoot memory is eliminated, and the dot pattern data iscreated easily.

It should be noted that there are may other modifications in the presentembodiment.

For example, one may eliminate the band memory 751 and store the cellstripe number N in the cell stripe memory 753 in the order of exposure.It is also possible to store the first relative address A·N or firstabsolute address A·N+B directly in the cell stripe memory 753.

Further, the circuit of FIG. 33 is applicable also to the first andsecond modifications of the present embodiment.

Further, the data compression of the exposure data of the presentembodiment is not limited to the BAA exposure system describedheretofore, but may be applicable also to other charged particle beamexposure systems such as the one that uses the electron beam scanningscheme shown in FIG. 34.

In the system of FIG. 34, it will be noted that the electron beam isdeflected in the direction D1 within a sub-field F1 and is movedstepwise in the direction D2, which is perpendicular to the primaryscanning direction D1, by the main deflector 720 by a width of thesub-field F1, wherein the direction D2 is coincident to the elongatingdirection of the stripe A5. Further, the stage 712 is drivencontinuously in a direction D3 perpendicular to the direction D2. Forexample, the stripe may have a length of 2 mm and the sub-field F mayhave a size of 100 μm for each edge.

[fifth embodiment]

In the BAA exposure system described heretofore, it is necessary toexpand the exposure data in the form of dot pattern data by software,while there are numerous exposure dots on the surface of the object.Thus, expansion of the dot pattern data requires substantial time, andit is necessary to increase the speed of data expansion as much aspossible. This problem of data expansion becomes particularly acute whenadjusting the boundary of exposure pattern with a minute amount as inthe case of compensating for the proximity effect by using a BAA masksuch as the one shown in FIG. 5, wherein the BAA mask carries thereon aplurality of aperture groups shifted in pitch by M/N, wherein N is thenumber of the aperture groups on the mask and M is an integer smallerthan N.

Conventionally, such a fine adjustment of the pattern boundary has beenachieved by canceling exposure of one or more dots in the vicinity ofthe pattern boundary, while such a cancellation of the exposure dotsrequires a substantial processing at the time of bitmap expansion. Forexample, such a calculation of the canceled exposure dots has to beconducted by taking the effect of pattern width and requires aprocessing conducted along the contour of the pattern boundary. Aboutthe fine adjustment of the exposure pattern by the BAA exposure systemthat has the foregoing M/N pitch-shift aperture groups, reference shouldbe made to the U.S. Pat. No. 5,369,282, which is incorporated herein asreference.

Accordingly, the present embodiment has an object of providing a chargedparticle beam exposure method and system that are capable of exposing apattern on an object at a high speed, without requiring particular dataprocessing with respect to pattern width or contour of the exposedpattern.

More specifically, the object of the present embodiment is to provide amethod and system for exposing an exposure pattern on an object by acharged particle beam, comprising the steps of:

shaping a charged particle beam into a plurality of charged particlebeam elements in response to first bitmap data indicative of an exposurepattern, such that said plurality of charged particle beam elements areselectively turned off in response to said first bitmap date;

focusing said charged particle beam elements upon a surface of anobject; and

scanning said surface of said object by said charged particle beamelements;

said step of shaping including the steps of:

expanding pattern data of said exposure pattern into second bitmap datahaving a resolution of n times (n≧2) as large as, and m times (m≧1) aslarge as, a corresponding resolution of said first bitmap data,respectively in X- and Y-directions;

dividing said second bitmap data into cells each having a size of 2nbits in said X-direction and 2m bits in said Y-direction; and

creating said first bitmap data from said second bitmap data byselecting four data bits from each of said cells, such that a selectionof said data bits is made in each of said cells with a regularity insaid X- and Y-directions and such that the number of rows in saidX-direction and the number of columns in said Y-direction are both equalto 3 or more.

According to the present invention, it becomes possible to achieve afine adjustment of the exposure pattern by using the first bitmap datawithout considering the effect of pattern width or conducting aprocessing along the contour of the pattern boundary. Thereby, theprocessing speed and hence the exposure throughput increasessubstantially.

In the description hereinafter, those parts described already withreference to previous embodiments are designated by the same referencenumerals and the description thereof will be omitted.

FIG. 35 shows the relationship between a bit data acquisition point anda corresponding beam spot point formed on the surface of the substrate710.

Referring to FIG. 35, a beam spot point is formed at the intersection ofa horizontal broken line and a vertical broken line and is designated byan open circle. In the description hereinafter, the beam spot point willbe designated as P_(ij), wherein the suffix i represents the number ofthe horizontal broken line, while the suffix j represents the number ofthe vertical broken line. It should be noted the beam spot pointcorresponds to the center of the exposure dot formed on the surface ofthe substrate 710. Thus, the exposure dots formed with a pitch of d formcorresponding rectangular exposure dots each having a size of 2d foreach edge.

Conventionally, the dot pattern data for a single exposure dot or "bitdata" is set to assume a logic value "1" in the interior of an exposurepattern, while the dot pattern data takes a logic value "0" in theoutside the exposure pattern. For example, the dot pattern data for apolygonal pattern having apex at points S1, S2, S7 and S8 includestherein the dot pattern data of logic value "1" at lattice points P24,P25, P34. P35, and P45.

In the present embodiment, on the other hand, the bit data for a bitdata acquisition point Q_(ij) represented by a solid circle, is used forthe beam spot point P_(ij), wherein the point Q_(ij) is shifted withrespect to the point P_(ij). Thereby, the shifting relationship betweenthe point Q_(ij) and P_(ij) is repeated for each cell C11. It will benoted that the cell C11 includes the exposure points P11, P12, P22 andP21 respectively locating at the four corners of a square 51 having asize d for each edge, while the points Q11, Q12, Q22 and Q21 are locatedat the apex of a rhomboid 52. Thereby, the point Q12 is set at anintermediate point between the points P12 and P22, while the point Q21is set an intermediate point between the point P21 and P22. Further, thepoint Q22 is set at a center of the points P22, P23, P33 and P32.

As the distance d is very small, typically 0.08 μm, the deformation ofthe pattern caused by deforming the square pattern 51 to rhombic pattern52 is negligible. While the deformation of the pattern appears at thepattern boundary, such a deformation includes a translational componentthat does not cause any substantial effect. After removing the effect ofsuch a translation, one obtains the actual effect of deformation thatcorresponds to a deformation from the rhombic pattern 52 to anotherrhombic pattern 53. The amount of translation, on the other hand, isgiven by a distance between any of the points R11, R12, R22 and R21 onthe rhomboid 53 and a corresponding apex of the square 51, wherein thedistance is equal for each of the foregoing points R11, R12, R22 and R21and is given by √2d/4=0.35d=0.028 μm. Thus, it will be noted that theeffect of the translational component associated with such an exposureis negligible, particularly in view of the blur caused in thephotoresist as a result of scattering within the resist.

FIG.35 further shows another rectangular pattern defined by corners S1,S2, 87 and S8, wherein the rectangular pattern includes the points P24,P25, P34, P35, P44 and P45 as the exposure dots. In the exposure of therectangular pattern, the data "1" for the bit data acquisition pointsQ24, Q25, Q34, Q44 and Q45 are used for exposing the forgoing pointsP24, P25, P34, P35, P44 and P45 respectively. Thereby, the rectangularpattern is exposed similarly as before.

On the other hand, when the width of the rectangular pattern isincreased by d/2, the rectangular pattern is now defined by the cornersS1, S3, S6 and S8, and the data "0" for the points Q26 and Q46 are usedfor the points P26 and P46, respectively. Thereby, the rectangularpattern thus formed have a reduced width as compared with the case ofconventional exposure in which the points P26 and P46 are both exposedwith the data "1."

With further increase in the width of the rectangular pattern by d/2,the rectangular pattern is defined by the corners S1, S4, S5 and 88, andthe data "1" for the bit data acquisition points Q26 and Q46 is used forexposing the dots for the points P26 and P46. Thereby, the width of therectangular pattern increases as compared with the pattern defined bythe corners S1, S3, S6 and S8.

Summarizing above, the present embodiment enables a fine adjustment ofthe exposure pattern by increasing or decreasing the exposure dots eachtime the width of the rectangular pattern is changed by an amount ofd/2. Further, the present embodiment eliminates the necessity ofadjusting the pattern in view of the pattern width or processing alongthe contour of the pattern.

It should be noted that any pattern that is exposed on the substrate bythe BAA exposure process can be decomposed into a rectangular patternand a right-angled triangle. FIG. 36 shows the change of the exposuredots in the case of such a right-angled triangle pattern, when the sizeof the triangle pattern is increased gradually in the map of FIG. 35.

Referring to FIG. 36, there is a triangle defined by corners T3, T4 andT5, wherein the present embodiment set the exposure data for the pointP34 to "0" in correspondence to the content of the data Q34. Otherwise,the exposure of the triangle is conducted similarly, and the pointsP_(ij) inside the triangle are set to the logic value "1" indicating theexposure.

When the size of the triangle is increased such that the triangle isdefined by the corners T2, T4 and T6, on the other hand, the data forthe point Q34 is used for the exposure of the point P34. Thereby, theexposed pattern of the triangle increases slightly. In the conventionalcase, such a slight increase in the size of the triangular pattern isnot possible.

With further increase of the triangle size as indicated by the patterndefined by the corners T1, T4 and T7, on the other hand, it will benoted that the number of the beam spots for exposing the triangular dotpattern increases by four, wherein this case is substantially identicalwith the conventional exposure of a triangular pattern.

Summarizing above, the present embodiment enables a fine adjustment ofthe exposure pattern by increasing or decreasing the exposure dots eachtime the size of an edge of the right-angled triangular pattern definingthe right-angled corner, is changed by an amount of d/2. It should benoted that the conventional exposure process causes the desired changeof the triangular pattern only when the size of the edge has changed byd. Further, the present embodiment eliminates the necessity of adjustingthe pattern in view of the pattern width or processing along the contourof the pattern.

FIGS. 37A-37D show the foregoing effect visually, wherein FIGS. 37A-37Dshow the relationship between the translation of the pattern boundaryand the bit data acquisition points for a cell C11 in FIG. 35.

Referring to FIG. 37A, it will be noted that the bit data acquisitionpoint increases one by one with the translation of the right edge of thepattern in the X-direction as X=0, 1, 3, 3, . . . , wherein the rightedge is parallel to the Y-axis as indicated by broken lines. A similarsituation occurs also for the left edge of the pattern.

In the example of FIGS. 37B-37D, on the other hand, the number of thebroken lines does not change with respect to the number of the lines(not illustrated), which lines are parallel to the broken lines andpassing through the open circles, while the foregoing advantageousfeature still holds in view of the surrounding cells shown in FIG. 35.Further, it should be noted that the exposure pattern used in the BAAexposure generally is primarily formed of rectangular patterns, with asmall number of triangular patterns. Thus, the exposure processaccording to the present embodiment is extremely useful for exposingexact exposure patterns with high efficiency.

FIG. 38 shows the construction of a data processing system used in theBAA exposure system that carries out the foregoing exposure.

Referring to FIG. 38, the data processing system includes a shoot memory841 provided inside the main control circuit 724 of FIG. 24, wherein apattern data disk 760, a data expansion unit 761, a canvas memory 762, abit shift circuit 763 and a bit map disk 764 cooperate with the maincontrol circuit 724. Thus, one can use a conventional bit map expansionunit provided in the system of FIG. 24, without substantialmodification. Further, the pattern disk 760 and the bit map disk 764have a storage capacity used conventionally in the BAA exposure system.The shoot memory 841 is a high speed bitmap memory typically formed of adynamic random access memory.

It should be noted that the pattern data disk 760 includes fundamentalpattern data including parameters and data that specifies theparameters, wherein the fundamental pattern data includes a codeindicative of the pattern shape and size data indicative of the size ofthe pattern.

The data expansion unit 761 reads out the pattern data from the disk 760and expands the same in the form of bit map, wherein the bit map thusexpanded is stored in the canvas memory 762. The bit map data thusexpanded assumes a logic value "1" when the data point falls inside thesquare pattern having a size of d/2 for each edge, while a logic value"0" when the data point falls outside the square pattern.

The bit shift circuit 763, on the other hand, decreases the bitmap datato 1/4 by eliminating unnecessary data and further causes a shift of thebit indicated in FIG. 36 by a solid circle to the position of thecorresponding open circle. The data thus shifted is stored in the bitmapdisk 764.

The data thus stored in the bit map disk 764 is read out, upon exposure,one block by one block and is held in the shooting memory 841.

FIG. 39A shows the bit map for two cells, wherein each division or boxin FIG. 39A corresponds to one bit of data. The data used for the actualexposure is stored in the box represented by a solid circle.

It will be noted that one obtains a symmetric bit map pattern shown inFIG. 39B by eliminating the data represented by the open circles,connecting a solid circle with a corresponding solid circle located at alower left direction thereof to form dot pairs, and shifting the dotpairs located at the left side in the upward direction by one division.

It should be noted that the bit shift circuit 763 utilizes the symmetricnature of the bit map shown in FIG. 39B and is constructed as indicatedin FIG. 39C, wherein FIG. 39C shows a case wherein one word of thecanvas memory 762 includes four bits in correspondence to the cellwidth, for the sake of simplicity. The canvas memory 762 is addressed bythe clock count of a counter 765.

In FIG. 39C, it should be noted that there is provided a two-bitregister 771 that causes the foregoing shift of the left side area ofthe bit map field in the upward direction by one bit. Further, there areprovided selectors 772A and 772B, wherein the selectors 72A and 72B areused for selecting the data represented by the solid circles in FIG.39B. The selectors 772A and 772B are supplied with respective controlsignals from a circulating shift register 73 running with a period oftwo bits, and the bit data selected by the selectors 772A and 772B isheld in a two-bit register 774. It should be noted that the clock issupplied to the shift register 773 and to the register 774 with a clockhaving a period twice as large as the clock supplied to the counter 765and to the register 771.

By using the bit shift circuit 763 having such a simple construction, itis possible to cause a shift of the data for the bit data acquisitionpoint indicated by the solid circles to the corresponding beam spotpoints represented by the open circles, at high speed. Further,unnecessary data is eliminated, and one can reduce the amount of data tobe 1/4 as compared with the case where no such a process is employed.

[first modification of the fifth embodiment]

In the foregoing fifth embodiment of the present invention, theseparation between the bit data acquisition points is set to d/2 forboth the X- and Y-directions, while it is possible to reduce theseparation further.

FIG. 40 shows the relationship between the bit data acquisition pointsand the corresponding beam spot points according to a first modificationof the fifth embodiment.

Referring to FIG. 40, four different cells, C11, C12, C22 and C21 aregrouped to form a cluster CL1, wherein the clusters thus defined arerepeated in rows and columns. It should be noted that cell C11 isidentical with the one shown in FIG. 35. Further, the bit dataacquisition points are disposed at the corners of the rhomboids7521-7524 that are identical in size and shape, wherein the rhomboid7522 is formed with a shift of d/4 in the downward direction withrespect to the rhomboid 7521, while the rhomboid 7524 is shifter to theleft with respect to the rhomboid by a distance of d/4. Further, therhomboid 7523 is shifted to the left with respect to the rhomboid 7522with a distance of d/4.

Similarly as in the case of FIG. 35, the data for the points Q11-Q44 areused for the exposure of the points P11-P44, respectively.

FIGS. 41A and 41B as well as FIGS. 42A and 42B show the relationshipbetween the translation of the pattern boundary and the data acquisitionpoint for one cluster shown in FIG. 40. As will be apparent from FIGS.41A and 41B, the number of the exposure dot increases in each of theclusters each time the pattern boundary, which is parallel to one of theY- and X-axes, moves by a distance of d/4. Thereby, it is possible toachieve a fine adjustment of the boundary of the exposure pattern.

In the case of FIGS. 42A and 42B, too, it will be noted that there arenine dotted lines passing in parallel through the solid circles, incontrast to the case where there are seven lines passing through theopen circles, wherein the representation of the seven lines are omittedfrom illustration. Thereby, one can achieve a fine adjustment of thepattern boundary. Although FIG. 42A and 42B show non-uniform separationof the dotted lines, it should be noted that there exist other dottedlines when the effect of surrounding clusters is taken intoconsideration, and the wide gap of the dotted lines is substantiallyreduced.

FIGS. 43A, 44A and 45A show rectangular patterns while FIGS. 43B, 44Band 45B show the corresponding exposure dots as well as the exposurepattern corresponding to the exposure dote.

Referring to FIGS. 43A and 44A, it will be noted that the pattern ofFIG. 44A is obtained by shifting the pattern of FIG. 43 in theX-direction by a distance of d/4. Similarly, the pattern of FIG. 45A isobtained by shifting the pattern of FIG. 44A in the X-direction by thedistance of d/4. From these drawings, it will be noted that the that theexposure pattern shifts by the distance of approximately d/4 each timethe rectangular pattern is shifted by the distance of d/4.

FIGS. 46A, 47A and 48A show the exposure of a triangular pattern, whileFIGS. 46B, 47B and 48B show the corresponding exposure dots used for theexposure of the triangular patterns.

Referring to FIGS. 46A and 47A, it will be noted that the pattern ofFIG. 47A is identical to the pattern of FIG. 46A except that the patternof FIG. 47A is shifted in the X-direction by a distance of d/4.Similarly, the pattern of FIG. 48A is identical to the pattern of FIG.47A except that the pattern of FIG. 48A is shifted in the X-direction bythe distance of d/4. It will be noted that the exposure pattern shiftsby approximately d/4 each time the rectangular pattern is shifted by thedistance of d/4.

FIG. 49A shows a bit map corresponding to one half of the cluster CL1 ofFIG. 40, wherein one division of FIG. 49A corresponds to one bit data.Similarly as before, the data actually used for the exposure is the bitmarked by a solid circle.

Referring to FIGS. 49A and 49B, one obtains the pattern of FIG. 49B byeliminating the open circles, connecting the solid circles generallyaligned in the vertical direction by respective continuous lines, andshifting the solid circles connected by the continuous lines at the leftside, in the upward direction by two bits. Thereby, a symmetricalpattern is obtained as indicated in FIG. 49B.

In this case, the construction shown in FIG. 49C is used, wherein thecircuit of FIG. 49C has a similar construction as in FIG. 49 andincludes a bit-shift circuit 63A in place of the bit-shift circuit 63,wherein it is assumed in FIG. 49C that the one word of the bit mapmemory includes eight bit data in correspondence to the cell width, forthe sake of simplicity.

Referring to FIG. 49C, there are provided four-bit registers 771A and771B arranged in two stages, wherein the registers 771A and 771b causesthe two-bit shift of the four-bit data corresponding to the left-half ofthe bit map field, in the upward direction. Further, there are providedselectors 772C and 772D for selecting the data designated by the solidcircles, wherein the selectors 772C and 772D are controlled by acirculating shift register 773A running with the period of four bits.The data selected by the selectors 772C and 772D is held in a two-bitregister 774.

The period of the clock supplied to the shift registers 73 and 74 is setfour times as large as the period of the clock supplied to the addresscounter 765 of the canvas memory 762A or to the registers 771A and 771B.

By using the simple construction of FIG. 49C, it is possible to transferthe data of the bit data acquisition point to the point of actualexposure at a high speed. Further, such a process eliminates unnecessarydata and the data is compressed by a factor of 1/16.

It is of course possible to construct the two-stage registers 771A and771B by using four two-bit shift registers. Further, one may use aquarternary counter and a detection circuit for detecting the count ofthe quaternary counter in place of the circulating shift register 773A.

[second modification of the fifth embodiment]

It should be noted that there are various selection of the clusters.

FIG. 50 shows the relationship between the bit data acquisition pointsand the beam spot points according to a second modification of the fifthembodiment.

Referring to FIG. 50, the cluster CL2 includes four different cells C11,D12, D22 and D21, wherein the cell C11 is identical to the one shown inFIG. 40. It should be noted that the bit data acquisition points arelocated, in each cell, at the corners of the rhomboids 7521, 7525-7527,wherein the rhomboids have an identical shape and size. It will be notedthat the rhomboid 7525 is shifted with respect to the rhomboid 7525 inthe upward direction by a distance d/4, the rhomboid 7527 is shiftedwith respect to the rhomboid 7521 to the right by a distance of d/4, andthe rhomboid 7526 is shifted with respect to the rhomboid 7525 to theright by a distance of d/4.

FIGS. 51A and 51B as well as FIGS. 52A and 52B show the relationshipbetween the translation of the pattern boundary and the data acquisitionpoints for one cluster in FIG. 50. As will be apparent from FIGS. 51Aand 51B, the shift of pattern boundary parallel to the Y- or X-axiscauses, in each cluster, an increase of the beam spots that actuallycauses the exposure of the dot pattern. Thereby, a fine adjustment ofthe exposure pattern becomes possible.

In the example of FIGS. 52A and 52B, the dotted lines are formed with auniform separation. It should be noted that there are nine dotted linespassing through the solid circles while this number is larger than thenumber of the lines (not shown) passing through the open circles in thedirection parallel to the dotted lines. This indicates the possibilityof fine adjustment of the pattern boundary as compared with theconventional exposure process. It should be noted that the blank areabetween the dotted lines also includes similar dotted lines, though notillustrated, wherein such additional dotted lines appear when the effectof the surrounding clusters are taken into consideration.

Further, the present embodiment includes various modifications for thecells, clusters as well as for the construction of the bit shiftcircuit. On may employ a construction to read out the data of the memorycell for the bit data acquisition points two-dimensionally by a singlereading step. Further, the construction of the present embodiment iseffective to the exposure system that uses the BAA mask shown in FIG. 4as well as the one shown in FIG. 5.

[sixth embodiment]

FIG. 53 shows a mask region 810 of a BAA mask 800 which is identical tothe BAA mask shown in FIG. 5, wherein it will be noted that the BAA mask800 carries thereon beam shaping apertures 801A arranged in rows andcolumns in the mask region 810, wherein a ground electrode 801 and ablanking electrode 802 are provided in each of the apertures 801A,similarly as before. The apertures 801A are grouped on the BAA maskregion 810 into two groups, one locating above a center line Cx and theother locating below the center line Cx, wherein the BAA mask 800 isdisposed so as to interrupt the electron beam emitted from the electrongun, and thus, the BAA mask region 800 is set in the BAA exposure systemsuch that the optical axis of the electron optical system passes througha point Co of the mask at which the foregoing center line Cx and avertical center line Cy of the BAA mask cross with each other.

In the BAA exposure system that uses such a BAA mask 800, the apertureslocated above the center line Cx induce an electric field a representedby an arrow heading in the downward direction when turning off theelectron beam elements formed by the apertures. On the other hand, theapertures located below the center line Cx induce an electric field B asrepresented by an arrow heading in the upward direction when turning offthe pertinent electron beam elements.

In the exposure process using such a BAA mask, there can be a case inwhich some of the electron beam elements produced by the BAA mask mayunwantedly pass through the round aperture when the electron beamelements are collectively deflected by a blanking deflector for turningoff the electron beam elements collectively as indicated in FIG. 54.

Referring to FIG. 54, the electron beam element such as the beam elementEB2 or EB3 produced as a result of shaping of an electron beam EB by theBAA mask region 810, misses the round aperture provided in a blankingplate 805, which corresponds to the blanking plate 113 of FIG. 3, uponenergization of an electrostatic deflector 804 that corresponds to theblanking deflector 116 of FIG. 3. Thereby, the beam elements EB2 and EB3are successfully turned off on the surface of a substrate that issubjected to the exposure.

On the other hand, when the electrostatic deflector 804 is notenergized, the electron beam elements produced by the BAA mask region810 travels along paths represented by EB1 or EB4, wherein the electronbeam element EB1 misses the round aperture on the blanking plate 805 andis turned off. Only the electron beam element EB4 passes through theround aperture and reaches the substrate.

In such an on-off control of the electron beam elements by theelectrostatic deflector 804, there some occurs a case in which anelectron beam element such as the electron beam element EB3, deflectedby the BAA mask region 810 so as to miss the round aperture in theblanking plate 805 is deflected back toward the optical axis Co as aresult of energization of the deflector 804, and unwantedly pass throughthe round aperture in the plate 805. When such a leakage of the electronbeam occurs, the exposure of desired pattern on the substrate is nolonger possible.

Thus, the present embodiment addresses the problem set forth above andprovides a BAA exposure system having a BAA mask wherein the deflectionof the electron beam elements is made in the same direction throughoutthe BAA mask.

Further, the present invention provides, in the present embodiment, aBAA exposure system having a BAA mask wherein the resistance andcapacitance of wiring used for carrying drive signals to theelectrostatic deflectors provided on the BAA mask, are optimized withrespect to the timing of turning on and turning off the apertures of theBAA mask.

More specifically, the present embodiment provides a charged particlebeam exposure system for exposing a pattern on an object, comprising:

beam source means for producing a charged particle beam;

beam shaping means for shaping said charged particle beam to produce aplurality of charged particle beam elements in accordance with exposuredata indicative of a dot pattern to be exposed on said object;

focusing means for focusing said charged particle beam elements upon asurface of said object; and

deflection means for deflecting said charged particle beam elements oversaid surface of said object;

said beam shaping means comprising:

a substrate formed with a plurality of apertures for shaping saidcharged particle beam into said plurality of charged particle beamelements;

a plurality of common electrodes provided on said substrate respectivelyin correspondence to said plurality of apertures, each of said pluralityof common electrodes being provided in a first side of a correspondingaperture; and

a plurality of blanking electrodes provided on said substraterespectively in correspondence to said plurality of apertures, each ofsaid plurality of blanking electrodes being provided in a second,opposite side of a corresponding aperture on said substrate.

Alternatively, the present embodiment provides a beam shaping mask forshaping a charged particle beam into a plurality of charged particlebeam elements, comprising:

a substrate formed with a plurality of apertures for shaping saidcharged particle beam into said plurality of charged particle beamelements;

a plurality of common electrodes provided on said substrate respectivelyin correspondence to said plurality of apertures, each of said pluralityof common electrodes being provided in a first side of a correspondingaperture; and

a plurality of blanking electrodes provided on said substraterespectively in correspondence to said plurality of apertures, each ofsaid plurality of blanking electrodes being provided in a second,opposite side of a corresponding aperture on said substrate.

Further, the present embodiment provides a process for fabricating abeam shaping mask for shaping a charged particle beam into a pluralityof charged particle beam elements, comprising the steps of:

providing a plurality of conductor patterns on a surface of a substratewith respective thicknesses such that at least one of said conductorpatterns has a thickness that is different from the thickness of anotherconductor pattern; and

providing a ground electrode and a blanking electrode on said substraterespectively in electrical contact with said conductor patterns, saidground electrode and said blanking electrode forming a deflector fordeflecting said charged particle beam elements.

According to the present embodiment set forth above, the beam shapingmask causes a uniform deflection when turning off the charged particlebeam, over entire area of the mask, and the problem of leakage of thedeflected charged particle beam elements upon the reversal deflectionupon the blanking of the charged particle beam is successfullyeliminated. Further, by optimizing the thickness and hence theresistance of the conductor patterns on the beam shaping mask, it ispossible to adjust the timing of activation of the individualelectrostatic deflectors formed on the beam shaping means forselectively turning off the charged particle beam elements.

FIG. 55 shows the principle of the BAA mask 800 according to the presentembodiment.

Referring to FIG. 55, the BAA mask 800 includes a substrate 823 formedwith a number of apertures 811A together with a common, ground electrode821 and an opposing blanking electrode 822, wherein the electrodes 821and 822 oppose with each other across the aperture 811A. Thereby, anumber of deflection units U₁, U₂, . . . Ui (i=1-n) are formed on thesubstrate 823 in a row and column formation in correspondence to theregion 810.

In order to drive the electrodes 821 and 822 on the BAA mask 800, thereis provided a wiring pattern 824 on the surface of the substrate 823such that the wiring pattern 824 extends toward the marginal part of thesubstrate 823, wherein the common electrode 821 and the blankingelectrode 822 are so disposed that the electric field induced by theelectrodes 821 and 822 acts in the same direction throughout thesubstrate 823 and hence the BAA mask. For this purpose, the electrodes822 are disposed in the same direction with respect to the correspondingelectrodes 821 throughout the BAA mask 800, wherein the cross section ofthe wiring patterns is optimized for adjusting the resistance andcapacitance of the wiring pattern and hence the signal delay caused inthe drive signals transmitted through the wiring pattern for activatingthe electrodes 822 of the apertures. It should be noted that theresponse time t of a circuit of finite length is given as

    t∞RCl.sup.2

wherein R represents the resistance of the circuit, C represents thecapacitance of the circuit, and l represents the length of the circuit.

FIG. 56 shows the construction of a BAA mask 800 of the presentembodiment in a schematical cross sectional view, while the mask region810 of the same BAA mask 800 is shown in FIG. 57 in a plan view.

Referring to FIG. 56, the BAA mask 800 is constructed on a boron-dopedsilicon substrate 823 that carries a surrounding rib or frame 811 formechanical reinforcement, wherein the apertures 811A are formed on thesubstrate 823 together with the ground electrodes 821 and blankingelectrodes 822 such that a ground electrode 821 faces a correspondingblanking electrode 822 across an aperture 811A.

Further, the substrate 823 carries a conductor pattern 824 for wiring aswell as a signal pad 825 and a ground pad 826.

As indicated in the plan view of FIG. 57, the electrodes 821 and 822 aredisposed so as to oppose with each other across each of the apertures onthe substrate 823 to form a deflection unit Ui, wherein there are in all1024 such deflection units Ui on the substrate 823. Typically, thesubstrate 823 may have a size of 3.2 mm×1.2 mm. The apertures 811A areformed on the substrate 823 in 64 columns in the direction of the Cyaxis and in 16 rows in the direction of the Cx axis. It will be notedthat there are in all 1024 apertures on the substrate 823.

In order to cause the desired deflection of the electron beam passingthrough the aperture 811A, the ground electrode 821 is connectedcommonly to the ground pad 826 shown in FIG. 56 together with otherground electrodes 821 on the substrate 823. Further, the blankingelectrode 822 is connected to the electrode pad 825 on the substrate 823via the conductor pattern 824 extending over the surface of thesubstrate 823.

In the present embodiment, the blanking electrode 822 is provided on thesame side of the ground electrode 821 throughout the substrate 823. Morespecifically, each of the blanking electrodes 822 is disposed at theright hand side (or left hand side) of the corresponding groundelectrode 821 throughout the substrate 823 and hence the BAA mask 800.

In such a construction of the BAA mask 800, it should be noted that theconductor pattern 824 is so formed that the signal delay caused in thedrive signal as it is propagating through the conductor pattern 824 fromthe electrode pad 825 to the aperture 811A, is successfully compensatedfor.

In order to achieve such a compensation of the signal delay, theinventor of the present invention has conducted an experiment formeasuring the resistance value of the conductor pattern 804 between theelectrode pad 805 to the blanking electrode 822 for each of theapertures 811A.

TABLE I shows the result thus obtained for the resistance value ofconductor patterns 824A provided on the BAA mask 800 in the regionlocated above the center line Cx.

                  TABLE I                                                         ______________________________________                                        electrode pad #                                                                              resistance (kΩ)                                          ______________________________________                                                   0       0.4                                                        824A       1       17                                                         above      2       17                                                         line Cx    3       21                                                                    4       24                                                                    5       23                                                                    6       21                                                                    7       20                                                                    8       16                                                                    9       14                                                                    10      17                                                                    11      20                                                                    12      21                                                                    13      23                                                                    14      21                                                                    15      20                                                                    16      16                                                                    17      20                                                                    18      17                                                         ______________________________________                                    

Similarly, the result of the following TABLE II was obtained forconductor patterns 824B provided on the area of the BAA mask 800 locatedbelow the line Cx.

                  TABLE II                                                        ______________________________________                                        electrode pad #                                                                              resistance (kΩ)                                          ______________________________________                                                   0       0.41                                                       824B       1       16                                                         below      2       20                                                         line Cx    3       27                                                                    4       23                                                                    5       24                                                                    6       22                                                                    7       19                                                                    8       14                                                                    9       17                                                                    10      20                                                                    11      27                                                                    12      25                                                                    13      24                                                                    14      26                                                                    15      17                                                                    16      14                                                                    17      19                                                                    18      20                                                         ______________________________________                                    

It should be noted that the foregoing measurement of the resistance wasmade by forming a blanking aperture array corresponding to the BAA mask800 on a semiconductor wafer shown in FIG. 58A and by providing the padelectrodes 825 on the marginal part of the wafer.

FIG. 58B shows the scheme of the foregoing resistance measurement,wherein there are in all 36 electrodes 825 on the upper and lower halvesof the upper major surface of the wafer, wherein the electrodes 825 arealigned along the left edge of the area corresponding to the BAA mask800, 18 of the electrodes being formed on the upper half region whilethe other 18 of the electrodes being formed on the lower half region.Further, the measurement of the resistance was made between an electrode825 and a corresponding electrode 822, wherein the electrodes 825 in theupper half region are connected to the corresponding electrodes 822 byway of the conductor patterns 824A, while the electrodes 825 in thelower half region are connected to the corresponding electrodes 822 byway of the conductor patterns 824B.

FIGS. 59A and 59B show the conductor patterns 824A and 824B in detail,wherein it will be noted that the conductor patterns 824B extend to therespective electrodes 825 along a path that circumvents the apertures811A, while the conductor patterns 824A extend to the respectiveelectrodes 825 more or less directly.

FIG. 58C shows the result of the resistance measurement thus conductedand represents the result of Tables I and II graphically, wherein thebroken line corresponds to the result of Table I while the continuousline corresponds to the result of Table II.

As already noted, the present embodiment adjusts the timing ofactivating the deflectors Ui by adjusting the resistance and capacitanceof the conductor pattern 824 that carries the drive signals to theelectrode 822 from the electrodes 825, wherein it should be noted thatthe electrodes 825 are provided in the marginal region of the substrate823 in correspondence to each of the deflectors Ui (i=1-1024). Each ofthe electrodes 821, 822, 825 and 826 is formed of a gold (Au) patternformed on the substrate 823.

Next, the function of the BAA mask 800 according to the presentembodiment will be described.

When an electron beam EB hits the lower major surface of the BAA mask800, the electron beam is shaped by the aperture as it passestherethrough and experiences a deflection in response to the deflectionvoltage applied across the electrodes 821 and 822, similarly to theconventional BAA mask.

In the BAA mask 800 of the present embodiment, on the other hand, itshould be noted that the electric field A₁, created by the deflectors U₁-U₅₁₂ located above the horizontal center line Cx, acts in the samedirection as the electric field A₂ that is created in the deflectorsU₅₁₃ -U₁₀₂₄, wherein the deflectors U₅₁₃ -U₁₀₂₄ are located in theregion below the center line Cx. Thereby, the electron beam elementsshaped by the BAA mask 800 is deflected in the same direction when theelectron beams are turned off, and the problem shown in FIG. 54 does notoccur. By forming the conductor pattern 824 to provide intentionalsignal delay, it is possible to align the timing of activation of thedeflectors Ui on the BAA mask 800.

Next, the fabrication process of the BAA mask 800 will be described withreference to FIGS. 60A-60H.

Referring to FIG. 60A, a doped silicon layer 812 and a silicon oxidefilm 813 are formed on a silicon substrate 811 of a predeterminedthickness, wherein the doped layer 812 may be formed by diffusing boronatoms into the silicon substrate 812 by a suitable process such as theion implantation process, typically for a thickness of about 15 μm. Thesilicon oxide film 813, on the other hand, may have a thickness of about5000 Å and is formed by a thermal annealing process of the siliconsubstrate 811 conducted in an oxidizing atmosphere.

Next, in the step of FIG. 60B, a contact hole is formed in the siliconoxide film 813 in correspondence to the ground pad 826, and conductorpatterns of Au are formed on the silicon oxide film including theforegoing contact hole for the ground pad 826. As will be described indetail later, the conductor patterns 814 may have various widths andthicknesses determined by the simulation about the signal delay causedtherein.

In the structure of FIG. 60B, it should be noted that the conductorpattern 814 may be formed on a film of TaMo that covers the surface ofthe silicon oxide film 813 with a uniform thickness of about 500 Å,wherein the TaMo film is formed by an electron beam deposition processfor improving the adherence of the conductor patterns 814 of AU on thesilicon oxide film 813. The conductor pattern 814 is thereby formed bydepositing a layer of Au upon the foregoing TaMo film by an electronbeam deposition process with a thickness of about 4500 Å. Further,another TaMo film is deposited on the Au layer with a thickness of about300 Å such that the foregoing Au layer is sandwiched vertically by apair of TaMo films.

After the structure of FIG. 60B is thus formed, a silicon oxide layer815 is deposited so as to bury the conductor patterns 814 underneath asindicated in FIG. 60C. Typically, the silicon oxide layer 815 is formedby a CVD process with a thickness of about 1500 Å. Further, the siliconoxide layer 815 as well as the silicon oxide layer 813 and theboron-doped layer 812 are subjected to a photolithographic patterningprocess in the step of FIG. 60D to form holes corresponding to theapertures 811A, wherein the holes are formed by an RIE (reactive ionetching) process with a depth of about 25 μm. Thereby, 1024 of suchholes are formed on the silicon substrate 811 in 8 rows and 128 columns.

Further, in the step of FIG. 60E, a resist layer is applied on thestructure of FIG. 60F, followed by a patterning of the same to form aresist pattern 831 that exposes the part of the silicon oxide layer 815in which various electrodes are to be formed. Further, the silicon oxidelayer 815 is patterned while using the resist pattern 831 as a mask, anda structure shown in FIG. 60E is obtained wherein the surface of theconductor pattern 814 is exposed in correspondence to contact holes815A.

Further, in the step of FIG. 60F, the resist pattern 831 is removed, anda conductor film 816 of TaMO/Au is deposited on the entirety of thesurface of the structure thus obtained, wherein the film 816 is formedof a TaMo layer and a Au layer thereon. The layer of TaMo is providedfor improving adherence of the Au layer.

Next, in the step of FIG. 60G, another resist layer is applied on thestructure of FIG. 60F, followed by a photolithographic patterningprocess to form a resist pattern 832, wherein it will be noted that theresist pattern 832 exposes the surface of the structure at contact holes815A' corresponding to the contact holes 815A. Further, anelectroplating process is conducted while using the conductor film 816as an electrode in the step of FIG. 60G, and conductor patterns such aspatterns 817A-817D are formed so as to fill the contact holes 815A'.Typically, the conductor patterns 817A-817D are formed by theelectroplating of Au.

After removing the resist pattern 832, a structure shown in FIG. 60H isobtained, wherein it will be noted that the conductor pattern 817Acorresponds to the ground electrode 821 of FIG. 56, the conductorpattern 817B corresponds to the blanking electrode 822, the conductorpattern 817C corresponds to the electrode pad 825,and the conductorpattern 827D corresponds to the ground pad 826. Further, the siliconsubstrate 811 is selectively removed with respect to the boron-dopedlayer 812 by an anisotropic etching process conducted by an EPW etchant,wherein the EPW etchant is an aqueous solution of ethylenediamine andpyrocatechol.

In the foregoing step of FIG. 60C, it should be noted that the conductorpatterns 814 are formed with respective optimized width and thickness soas to optimize the timing of the signals carried by the conductorpatterns 814. In order to adjust the thickness of the conductor patterns814, the present embodiment employs the process shown in FIGS. 61A-61D.

Referring to FIG. 61A, a resist pattern 818 is formed on a conductorlayer, which forms the pattern 814 upon patterning, wherein theconductor layer may include an Au layer sandwiched vertically by a pairof TaMo films. Further, a resist layer is deposited on the conductorlayer, followed by a patterning of the same by using a reticle L1 toform a resist pattern 818. Further, the conductor layer is patterned byusing the resist pattern 818 as a mask to form the foregoing conductorpatterns 814.

Next, in the step of FIG. 61B, the resist pattern 818 is removed andanother conductor pattern also of an Au layer sandwiched by a pair ofTaMo films is deposited on the silicon oxide film 813 so as to bury theconductor patterns 814 already formed in the step of FIG. 61A. Further,the conductor layer thus deposited is subjected to a photolithographicpatterning process using e second reticle L2, wherein a new conductorpattern 814 is formed on the surface of the silicon oxide film 813 aswell as on the conductor patterns 814 already formed on the siliconoxide film 813.

By repeating a similar step by using a third reticle L3, one obtains astructure of FIG. 61C wherein the patterns 814 on the silicon oxide filmare formed with three, different thicknesses.

Further, in a step of FIG. 61D, are resist pattern 818 is formed so asto protect the exposed surface of the silicon oxide film 813 by areticle L4, and the conductor patterns 814 are subjected to an ionmilling process for fine adjustment of the thicknesses, such that thedesired delay is guaranteed for the signals carried by the conductorpatterns 814.

In such a process for changing the pattern thickness intentionally, itis also possible to change the pattern thickness in correspondence to aparticular part of the pattern as indicated in FIGS. 62A and 62B,wherein FIG. 62A shows a part of the conductor pattern 824 formed withrespective pattern thicknesses corresponding to the state of FIG. 61D,while FIG. 62B shows a state in which the thickness is changed for apart of one of the conductors by using a reticle L5. FIG. 62C shows apart of FIG. 62B in an enlarged scale.

Further, one may form the conductor patterns 814 having differentthicknesses according to the process of FIGS. 63A-63C, wherein reticlesL6-L8 forming a negative meek are used. In such a case, patterns 814 aredeposited on the silicon oxide film 813 in the step of FIG. 63A whileusing the reticle L6, followed by a process for depositing furtherconductor patterns 814 in the step of FIG. 63B, wherein the step of FIG.63B is conducted by using the reticle L7 that causes a deposition of theconductor selectively on one of the conductor patterns already formed onthe silicon oxide film 813. Further, by conducting the step of FIG. 63Cby using the reticle L8, it is possible to form the conductor patterns814 with three different thicknesses.

FIG. 64 shows a BAA exposure system that uses the BAA mask 800, whereinit will be noted that the BAA exposure system includes an electron gun839 that produces an electron beam along an optical axis toward asubstrate 846 held on a movable stage (not shown), wherein the BAA mask800 is disposed so as to interrupt the path of the electron beam fromthe electron gun 839. Thereby, the BAA mask 800 produces a plurality ofelectron beam elements as a result of shaping of the electron beam,wherein the electron beam elements thus produced are focused upon thesubstrate 846 by means of electron lenses 843 forming a demagnificationsystem. Further, the electron beam elements are moved over the surfaceof the substrate 846 by means of electrostatic as well aselectromagnetic deflectors 844.

In order to turn off the electron beam elements collectively on thesurface of the substrate 846, the BAA exposure system of FIG. 64 usesthe blanking deflector 804, wherein the blanking deflector 804 deflectsthe electron beam elements collectively away from the optical axispassing through the round aperture formed on the blanking plate 805.Thereby, the BAA mask 800 is disposed with an orientation such that theelectron beam elements are deflected at the deflectors on the BAA mask800 in the same direction as the direction of beam deflection caused bythe blanking electrode 804. Thereby, the problem of the turned-offelectron beam elements leaking through the round aperture in the plate805 upon the energization of the blanking electrode 804 is effectivelyeliminated.

[seventh embodiment]

In the BAA exposure system described heretofore, there sometimes occur aneed for removing the BAA mask for inspection or maintenance. Thus, inorder to hold the BAA mask removably, conventional BAA exposure systemsgenerally employ the construction of FIG. 65.

Referring to FIG. 65, there is provided a printed circuit board 915within an evacuated column 912 of the electron optical system so as tointersect with the path of the electron beam produced by an electron gun913 and traveling toward a substrate 914, wherein the printed circuitboard 915 is provided with a passage of the electron beam 915x. Theprinted circuit board 915 supports thereon a socket 923 having a similarpassage 923x of the electron beam, wherein a package body 919 of a BAAmask 911 is mounted upon the socket 923.

Thus, the printed circuit board 915 is formed with a number of holes915a for accommodating electrode pins of the socket 923, and conductorpatterns 915b are provided on the upper major surface of the board 915for connecting the foregoing holes 915a electrically to respectiveinterconnection pads provided also on the upper major surface of theprinted circuit board 915. In order to supply electrical signals to theBAA mask, a number of lead wires 916 are provided such that the wires916 extend from a signal generator 918 outside the evacuated column 912to the corresponding interconnection pads on the printed circuit board915 via a hermetic seal 917 provided on the wall of the column 912.

The socket 923 is fixed upon the printed circuit board 915 by insertingthe electrode pins thereof into corresponding holes 915a on the board915 and soldering the electrode pins against the electrode patterns915b, while the socket 923 in turn supports the package body 919 thereonremovably such that electrode pins on the package body 919 are acceptedremovably into the corresponding holes on the socket 923. It should benoted that the holes on the socket 923 are connected electrically torespective electrode pins that project from the socket 923 forengagement with the corresponding holes 915a on the printed circuitboard 915.

The package body 919 also has a passage 919x of the electron beam inalignment with the holes 915x and 923x, wherein the package body 919carries a chip or substrate in which the BAA mask 911 is formed.Hereinafter, the chip of the BAA mask will be designated by thereference numeral 911. The chip 911 is bonded upon the lower majorsurface of the package body 919 by means of adhesives so as to intersectthe path of the electron beam passing through the passage 919x. Thus, byactivating electrostatic deflectors 921 provided in correspondence to aplurality of beam shaping apertures on the chip 911, the electron beamelements produced by shaping the electron beam by the beam shapingapertures, are selectively turned off. It should be noted that theelectrostatic deflectors 921 on the chip 911 are connected electricallyto corresponding electrode pads 920 provided on the package body 919 bymeans of bonding wires 922 such that the bonding wire connects anelectrode pad on the BAA chip 911 to a corresponding electrode pad 920,which pad 920 in turn being connected electrically to a pin of thepackage body 919,

When dismounting the BAA chip 911 in such a construction of the BAAexposure system, it is necessary to remove the package body 919 from thesocket 923, which is fixed upon the printed circuit board 915. On theother hand, because of the large number of pins of the package body 919inserted into the socket 923 with a substantial force for reliableelectrical contact, there is a substantial difficulty in such a processof dismounting. Particularly, the operation for mounting and dismountingthe BAA package body 919 inside the evacuated column 912 is virtuallyimpossible.

In view of such a situation, such a mounting/dismounting process hasbeen conducted outside the evacuated electron beam column 912. Morespecifically, the vacuum inside the column 912 is broken, and theprinted circuit board 915 is taken out from the column 912 within anallowable distance of the wires 916. Thus, the mounting and dismountingof the BAA package body 919 is carried out outside the column 912. Onthe other hand, such a process has an obvious drawback in that it isnecessary to carry out the evacuation of the column 912 upon reassemblyof the package body 919 on the socket 923, by activating a vacuum pumpfor a prolonged duration.

Thus, the present embodiment addresses this problem and has an object ofproviding a BAA exposure system in which the foregoing problems areeliminated.

More specifically, the present embodiment provides a BAA exposure systemin which maintenance of the BAA mask is substantially facilitated.

Thus, the present embodiment provides a charged particle beam exposuresystem for exposing a pattern on an object by a charged particle beam,comprising:

beam source means for producing a charged particle beam, said beamsource means emitting said charged particle beam toward an object onwhich a pattern is to be exposed, along an optical axis;

beam shaping means for shaping said charged particle beam to produce aplurality of charged particle beam elements in accordance with exposuredata indicative of a dot pattern to be exposed on said object;

focusing means for focusing said charged particle beam elements upon asurface of said object; and

deflection means for deflecting said charged particle beam elements oversaid surface of said object;

said beam shaping means comprising:

a beam shaping mask carrying thereon a plurality of apertures forproducing a charged particle beam element by shaping said chargedparticle beam and a plurality of deflectors each provided incorrespondence to one of said plurality of apertures, said beam shapingmeans further including a plurality of electrode pads each connected toa corresponding deflector on said beam shaping means;

a mask holder provided on a body of said charged particle beam exposuresystem for holding said beam shaping mask detachably thereon, said maskholder comprising: a stationary part fixed upon said body of saidcharged particle beam exposure system; a movable part provided movablyupon said stationary part such that said movable part moves in a firstdirection generally parallel to said optical axis and further in asecond direction generally perpendicular to said optical axis, saidmovable part carrying said beam shaping mask detachably; a drivemechanism for moving said movable part in said first and seconddirections; and

a contact structure provided on said body of said charged particle beamexposure system for contacting with said electrode pads on said beamshaping mask, said contact structure including a base body and aplurality of electrode pins extending from said base, said of saidelectrode pins having a first end connected to said base body of saidcontact structure and a second, free end adapted for engagement withsaid electrode pads on said beam shaping mask.

According to the construction of the present embodiment, particularlythe construction of the beam shaping mask held on the mask holder andthe construction of the cooperating contact structure, it is possible todismount the BAA mask easily, without breaking the vacuum inside theelectron beam column. Thus, the time needed for maintenance of the BAAmask is substantially reduced, and the throughput of exposure increasessubstantially. Further, the BAA exposure system of the presentembodiment is advantageous in the point that one can use various beamshaping masks by simply dismounting an old mask and replacing with a newmask. Thereby, the charged particle beam exposure system of the presentinvention is not only useful in the BAA exposure system but also in theblock exposure system.

FIG. 66 shows the overall construction of a BAA exposure system 930 ofthe present embodiment.

Referring to FIG. 66, the BAA exposure system 930 includes an electrongun 934 provided in evacuated electron beam column 931 for emitting anelectron beam, wherein the electron beam thus produced is focused, byelectron lenses 936 and 937, upon a BAA mask 948 mounted detachably on aprobe fixture 948 provided inside the column 931. As will be describedin detail later, the BAA mask 948 is held movably by a mountingmechanism 947.

The BAA mask 948 produces a plurality of electron beam elementssimilarly as other BAA exposure systems by shaping the incident electronbeam by the beam shaping apertures provided thereon, wherein theelectron beam elements thus produced are focused upon a substrate 970held on a movable state 935 by electron lenses 938-940 forming ademagnifying optical system. Further, there is provided a deflector 943inside the column 931 for causing a deflection of the electron beamelements over the surface of the substrate 970 on the stage 935.

In order to turn off the electron beam elements on the surface of thesubstrate 970, there is provided a blanking plate 945 formed with around aperture or blanking aperture in cooperation with a blankingdeflector 944 that deflects the electron beam elements away from theround aperture on the blanking plate 945 when turning off the electronbeam elements collectively on the surface of the substrate 970.

In order to control the BAA exposure system 930 of FIG. 66, there isprovided a control system 933 that includes a control circuit 952 forproducing a drive signal for each of the beam deflectors provided on theBAA mask 948 in correspondence to the apertures thereon. Uponenergization of the beam deflector on the BAA mask 948, the electronbeam element shaped by an aperture on the BAA mask 948 is deflected awayfrom the optical axis and misses the round aperture on the blankingplate 945 as indicated by a beam 972. When the beam deflector on the BAAmask 948 is not energized, on the other hand, the electron beam elementpasses through the round aperture and forms an image of the aperture ofthe BAA mask 948 on the substrate 970 with a demagnification. Further,there is provided a blanking control circuit 984 for turning off theelectron beam elements collectively by supplying a drive signal to theblanking electrode 944. Furthermore, the control system 933 includes ascanning controller 953 that controls the deflector 943 as well as themovable stage 935 for causing the electron beam elements to scan overthe surface of the substrate 970. In order to control the foregoingvarious circuits, there is provided a central processing unit (CPU) 950that cooperates with a memory 991.

FIGS. 67 and 68 show the construction of the probe assembly 946 shown inFIG. 66.

Referring to FIGS. 67 and 68, it will be noted that the probe assembly946 includes an annular base 980 of a multilayer substrate held upon awall 987 forming a part of the electron beam column 930 with hermeticseal provided by seal elements 990 and 991.

The annular base 980 carries thereon a number of probe electrodes 982each having an end soldered upon a corresponding electrode pad 983provided on the upper major surface of the base 980, wherein the probeelectrodes 982 extend, via a support member 981, generally in adirection toward a central axis of the annular base 980 to formcollectively a conical surface. Thereby, each of the probe electrodes982 has a free end 982a at an end opposite to the end soldered upon theelectrode pat 983 as indicated in FIG. 68, wherein the free ends 982a ofthe probe electrodes 982 support the BAA mask 948 mechanically byengaging with corresponding electrode pads 1034 that are provided on alower major surface of the BAA mask 948.

Further, there are provided additional probe electrodes 992 and 993 fordetecting the proper mounting of the mask 48, wherein the probeelectrodes 992 and 993 have respective ends 992a and 993a engaging withcorresponding electrode pads 1038 and 1039. It should be noted that theelectrode pads 1038 and 1039 are connected with each other electricallyby a bridging pattern 1040 provided on the lower major surface of theBAA mask 948. In FIG. 68, it will be noted that the BAA mask 948 carriesapertures 1031 with corresponding blanking electrodes 1032 and a commonground electrode 1033. Further, FIG. 68 shows a marginal region 989 ofthe annular base 980 that engages with the seal members 990 and 991. Itwill be noted that there are bonding pads 985 disposed outside theforegoing region 989, for connection to lead wires 986 extending to thecontrol circuit 952.

FIGS. 69-72 show the construction of the mounting mechanism 947 indetail, wherein FIG. 69 shows the mechanism 947 in a plan view, FIG. 70shows the same mechanism 947 in a side view as viewed from the directionZ₁ -Z₂. Further, FIG. 71 shows the same mechanism in a side view asviewed in a direction perpendicular to the direction of FIG. 70, whileFIG. 72 shows the mechanism 947 in a bottom view.

Referring to FIGS. 69-72, it will be noted that the mounting mechanism947 is constructed upon a base body 1000 fixed upon the column 931 ofthe BAA exposure system 930, wherein the base body 1000 carries thereona rectangular frame 1003 on which a pair of guide rods 1002a and 1002bare provided to extend in the X-direction, wherein the guide rods 1002aand 1002b carry thereon a first movable stage 1003 such that the stage1003 is movable, upon energization of a drive mechanism 1004, in theX₁ - and X₂ -directions within a range between a position P₁ and aposition P₂. Further, the movable stage 1003 carries thereon fourbearing mechanisms 1005 each including a vertical shaft 1006 that passesthrough the bearing mechanism 1005 wherein the shafts 1006 are movablein the Z₁ - and Z₂ -directions.

On the lower end of the foregoing shafts 1006, a second stage 1008 isfixed such that the stage 1008 is movable in the Z₁ - and Z₂ directionstogether with the shafts 1006, wherein the stage 1008 carries on a lowermajor surface thereof a shallow depression 1007 for accommodating aholder 1015 of the BAA mask 948. It should be noted that the holder 1015holds the BAA mask 948 unitarily. Further, a return spring 1009 isprovided on each of the shafts 1006 for urging the stage 1008 in thedownward direction. The stage 1008 moves thereby between a lowermostposition Q₁ and an uppermost position Q₂ shown in FIG. 70, wherein sucha movement of the stage 1008 is caused by a vertical drive mechanism1010.

It should be noted that the drive mechanism 1004 for driving the stage1003 in the X-direction includes a rack 1011 formed on the X-stage 1003as indicated in FIG. 69 as well as a pinion gear 1012 engaging with therack 1011, wherein the pinion gear 1012 is driven by a motor notillustrated. On the other hand, the drive mechanism 1010 for the stage1008 includes eccentric cams 1014a and 1014b formed on a shaft 1013a aswell as eccentric cams 1014c and 1014d formed on a shaft 1013b, whereinthe cams 1014a-1014d cooperate with the corresponding shafts 1006respectively and causes the same to move in the upward and downwarddirections. The illustration of the drive motor for driving the shafts1006 will be omitted for the sake of simplicity.

Thus, in the construction of the BAA exposure system 930 of the presentembodiment, it will be noted that the BAA mask 948 is movable in thevertical as well as lateral directions together with the stage 1008 ofthe mounting mechanism 947, wherein the mask 948 engages with the probeelectrodes 982 provided inside the column 931 when the BAA mask 948 ismoved to the position P₁ at the center of the column 931 as a result ofenergization of the drive shafts 1002a and 1002b and is fully lowered tothe level Q₁ as a result of energization of the drive shafts 1013a and1013b.

In the BAA exposure system 930 of FIG. 66, it will be noted that thestage 1008 and hence the BAA mask 948 mounted thereon is lifted up,together with the holder 1015, to the level of Q₂ and is moved furtherto the position P₂ close to a sub-chamber 932, wherein the sub-chamber1032 is separated from the column 931 by a gate valve 960. It should benoted that the BAA mask 948 is disengaged from the probe electrodes 982on the base 980 upon lifting from the level Q₁ to the level Q₂, whereinthe level Q₂ is about 2 mm higher than the level Q₁. Further, thesub-chamber 932 is separated from the surroundings by another gate valve961.

Thus, the dismounting of the BAA mask 948 is conducted in the BAAexposure system 930 of the present embodiment by moving the stage 1008to the level Q₂ and the position P₂ shown in FIG. 69 by first activatingthe drive shafts 1013a and 1013b of FIG. 70, followed by activating thepinion gear 1012 shown in FIG. 69. In this state, the holder 1015 movesfrom a position S₂ to a position shown in FIG. 70 by S₁.

It should be noted that the stage 1008, on which the holder 1015 ismounted detachably, is formed with a rail portion 1008R for holding arim part of the holder 1015 as indicated in FIG. 71, wherein it shouldbe noted that FIG. 71 is a cross section of the structure of FIG. 69taken along a line VI--VI and viewed from the direction of the arrows.Thus, the holder 1015 is held on the stage 1008 movably in theX-direction and hence can be pulled out in the X₁ direction or insertedin the X₂ direction by using a suitable jig 1020. The jig 1020 has a rod1021 on which an actuation head 1022 is formed and is provided in thesub-chamber 932 such that the jig 1020 can be inserted into the interiorof the column 931 upon release of the gate valve 960. In order to engagewith the actuation head 1022 of the jig 1020, the holder 1015 is formedwith a cutout 1015a corresponding in size and shape with the actuationhead 1022.

Thus, when replacing the BAA mask 948 in the BAA exposure system 930 ofFIG. 66 with another similar BAA mask, the sub-chamber 932 is firstevacuated to the degree of vacuum comparable to the interior of thecolumn 931. Simultaneously, the stage 1003 as well as the stage 1008 areactivated such that the stage 1008 moves from the level Q₁ to the levelQ₂ and such that the stage 1003 is moved from the position P₁ to theposition P₂. As a result, the BAA mask 948 moves, together with theunitary holder 1015, from the position S₁ to the position S₂.

Next, the gate valve 960 is opened, and the jig 1020 is inserted to theinterior of the column 931, such that the head 1022 engages with thecorresponding cutout 1015a on the holder 1015. Further, by pulling thejig 1020, the BAA mask is removed, together with the holder 1015, fromthe stage 1008. In the state that the jig 1020 and the holder 1015 areheld in the sub-chamber 932, the gate valve 960 is closed, and thevacuum of the sub-chamber 932 is broken. After the pressure inside thesub-chamber 932 has reached the environmental pressure, the gate valve961 is opened, and the BAA mask 948 is taken out to the environmenttogether with the holder 1018.

When replacing the old BAA mask 948 with a new one, a new holder 1015holding a new BAA mask 948 is mounted upon the jig 1020 inside thesub-chamber 932. After closing the gate valve 961, the sub-chamber 932is evacuated by activating a pump 962 while maintaining the closed stateof the gate valve 960. After the pressure inside the sub-chamber 932 isequilibrated with the internal pressure of the column 931, the gatevalve 960 is opened and the holder 1015, held on the end of the jig1020, is inserted to the column 931 such that the holder 1015 isinserted into the holder 1008 that is already moved to the position P₁and is held at the level Q₁. Thereby, the holder 1015 engages with therail part 1008R of the stage 1008 and is held at the position S₁.Further, the pinion gear 1012 is activated to drive the stage 1003 tothe position P₂, followed by the activation of the drive shafts 1013aand 1013b to cause a lowering of the stage 1008 to the level Q₂.

In this process, it should be noted that the high quality vacuum ismaintained in the column 931 throughout the process for replacing theBAA mask, and the maintenance of the BAA exposure system is completedwith a substantially reduced time. Upon lowering of the BAA mask 948 tothe level S₁. the probe electrodes 982 establish an engagement withcorresponding pads 1034 on the mask 948 with reliability. Further, anyabnormality in the mounting state of the BAA mask 948 is immediatelydetected checking the conductance between the probe electrode 992 andthe probe electrode 993. The number of such detection electrodes 992 and993 is of course not limited to two but three or more electrodes may beformed.

FIG. 73 shows the construction of the BAA mask 948 used in the presentembodiment in a bottom view.

Referring to FIG. 73, it will be noted that the BAA mask 948 includes anumber of rectangular beam shaping apertures 1031 formed on a substrate1030 in rows and columns with a predetermined pitch, wherein thesubstrate 1030 is defined by edges 1030a-1030d, and there are provided anumber of electrode pads 1034 on the lower major surface of thesubstrate 1030 such that the electrode pads 1034 surround the regionwherein the apertures 1031 are formed. Typically, the electrode pads1034 are formed with a staggered relationship, wherein the illustratedexample uses four rows 1035₁ -1035₄ of the electrode pads 1034 alongeach of the edges 1030a-1030d. Each of the electrode pads 1034 areconnected to a corresponding blanking electrode 1032 by a conductorpattern 1036, wherein the blanking electrodes 1032 are disposed so as toface a common ground electrode 1033 across a pertinent aperture 1031.

It should be noted that each of the pads 1034 has a size a of 0.2 mm inthe direction of the pertinent edge such as the edge 1030a and a sizebof 0.3 mm in the direction perpendicular to the edge 1030a, wherein thesize of the edge b is set larger than the size of the edge a in view ofthe elastic deformation or bending of the electrode probes 982 whenlowering the mounting of the BAA mask 948 from the level Q₂ to Q₁.Further, the substrate 1030 carries on the lower major surface thereoftest patterns 1037₁ -1037₃ respectively on corners 1030e-1030g fordetecting anomalous mounting state of the BAA mask 948. Each of the testpatterns such as the test pattern 1037₁ includes a pair of electrodepads 1038 and 1039 connected by a bridging pattern 1040. On the otherhand, no such a test pattern is formed on a corner 1030h, wherein thecorner 1030h is used for handling the BAA mask 948.

[modification of the seventh embodiment]

It should be noted that the present embodiment is by no means limited tothe BAA mask 948 of FIG. 73 but may be applied to other beam shapingmasks such as a mask 1050 shown in FIG. 74.

Referring to FIG. 74, the beam shaping mask 1050 is formed on a siliconsubstrate 1041 and includes generally C-shaped openings 1051 in place ofthe array of the square apertures 1031, wherein the mask 1050 includeselectrostatic deflectors 1052 and 1053 provided adjacent to the C-shapedopening 1051 on the surface of the silicon substrate 1041, such that theelectrostatic deflectors 1052 and 1053 are connected to respectiveelectrode pads 1034 formed on the marginal part of the substrate 1041.

FIGS. 75-75D show the examples of the pattern exposed on a substrate bythe electron beam shaped by the opening 1051 for various combination ofthe drive signals supplied to the electrostatic deflectors 1052 and1053. It will be noted from FIGS. 75A-75D that one obtains variouspatterns 1055₁ -1055₄ by using the same mask 1050, by merely changingthe combination of the drive signals supplied to the electrostaticdeflectors.

It should be noted that beam shaping mask of FIG. 74 has variousadvantageous features over the beam shaping masks used in theconventional BAA exposure process or block exposure process in that:

(a) versatile patterns can be produced from a single beam shapingaperture;

(b) switching of the patterns from one pattern to a next pattern can beachieved in the order of several nanoseconds. Thus, one can achieveexposure of versatile patterns with a high throughput;

(c) fine patterns can be formed with higher precision as compared withthe BAA process.

FIG. 76 shows a beam shaping mask 1060 as another example of theforegoing modification, wherein it will be noted that the mask 1060includes a beam shaping aperture 1061 having a zigzag form. The aperture1061 is provided with electrostatic deflectors 1062 and 1063, whereineach of the deflectors is connected to a corresponding electrode pad1034 formed on the marginal area of the beam shaping mask 1060 so as tosurround the apertures on the central part.

Next, a description will be given on the electron beam exposure systemthat is suitable for use in combination with the beam shaping mask ofFIG. 74 or FIG. 76, particularly the mask 1060 of FIG. 76. In thedescription hereinafter, those parts described previously with referenceto preceding embodiments are designated by the identical referencenumerals and the description thereof will be omitted.

When using the beam shaping mask 1060 of FIG. 76 in the BAA exposuresystem of FIG. 66, it will be noted that the direction of the beamdeflection caused by the mask 1060 is different from the case in whichthe beam shaping mask 948 of FIG. 73 or the beam shaping mask 1050 ofFIG. 74 is used. Thus, there can be a case similar to the one discussedpreviously with reference to FIG. 54 in which the electron beamdeflected by the beam shaping mask 1060 may experience unwanteddeflection for deflecting back the electron beam, shaped by the beamshaping mask 1060, toward the optical axis. In such a case, the electronbeam deflected by the electrostatic deflector on the beam shaping mask1060 may not be completely interrupted by the blanking plate 945.

In order to avoid this problem in the BAA exposure system of FIG. 66,which is designed to use various beam shaping masks, the presentmodification uses an electron beam exposure system of FIG. 77 which issimilar to the BAA exposure system of FIG. 66 except that it uses ablanking fixture 1081 shown in FIG. 78.

Referring to FIG. 78, there are three blanking electrodes 1082-1084 inthe blanking fixture 1081 for deflecting the electron beam away from theround aperture provided in the blanking plate 945. In the blankingfixture of 1081 of FIG. 78, it will be noted that the electrode 1084 isgrounded while the electrodes 1082 and 1083 are supplied with respectivedrive signals from the blanking control circuit 954, such that theblanking fixture 1081 causes the deflection of the electron beam in anoptimum direction for interrupting the electron beam, which has alreadybeen deflected by the beam shaping mask 1060, positively by the blankingplate 945.

FIG. 79 shows the deflection of the electron beam in the electron beamexposure system of FIG. 77 on the blanking plate 945, wherein theblanking plate 945 carries a round aperture 945a coincident to theoptical axis of the electron optical system of the electron beamexposure system. Referring to FIG. 79, it will be noted that theelectron beam, deflected by the beam shaping mask 1050 of FIG. 74 in thedirection of an arrow 1071, is further deflected in the same directionas represented by an arrow 1087, by optimizing the drive voltagesapplied to the electrodes 1082 and 1083. Similarly, the electron beamdeflected by the beam shaping mask 1060 of FIG. 76 in the direction ofan arrow 1070, is further deflected in the same direction as representedby an arrow 1086, by optimizing the drive voltages applied to theelectrodes 1082 and 1083.

In order to indicate the direction of the beam deflection caused by thebeam shaping mask, the electron beam exposure system of FIG. 77 uses aninput device 1085 that provides information about the direction of thebeam deflection caused by the beam shaping mask to the CPU 950. The CPU950 in turn controls the blanking control circuit 954 such that theelectron beam deflected by the beam shaping mask is further deflected bythe blanking electrode 944 in the same direction. Thereby, the blankingcontrol circuit 954 changes the ratio of the voltages applied to theelectrodes 1082 and 1083 in response to the specified direction of thebeam deflection.

[eighth embodiment]

Next, an eighth embodiment of the present invention will be described.

In order to reduce the fabrication cost of semiconductor devices, it isadvantageous to form the semiconductor devices on a large diameterwafer. This principle applies also to the BAA exposure system.

Thus, in order to expose a large diameter substrate such as a wafer of1112 inches diameter, there is proposed a BAA exposure system 1110 shownin FIG. 80 that uses three electron beam columns 1111₁ -1111₃ disposedsuch that the electron beam columns 1111₁ -1111₃ expose together asingle substrate 1112. The electron beam columns 1111₁ -1111₃ includerespective electron guns and electron optical systems includingdeflection systems, in addition to respective BAA masks 1113₁ -1113₃,wherein a plurality of BAA controllers 1115₁ -1115₃ are provided forcontrolling the BAA masks 1113₁ -1113₃ respectively. Further, the BAAcontrollers 1115₁ - 1115₃ cooperate with corresponding control systems1114₁ -14₃, wherein the control systems 1114₁ -1114₃ expand and supplydot pattern data indicative of the exposure dots to be formed on thesubstrate 1112, to respective BAA controllers 1115₁ -1115₃, based uponthe exposure data from an external control system 1116.

In such a construction of the BAA exposure system, it should be notedthat the each of the controllers 1115₁ -1115₃ has a construction such asthe one described already with reference to FIG. 3. Similarly, each ofthe control systems 1114₁ -1114₃ has a construction shown also in FIG.3. Thus, the BAA exposure system of FIG. 80 inevitably has a large andcomplex construction, which is disadvantageous for fabricatingsemiconductor devices with low cost. It should be noted that the BAAexposure system having a single column and hence using a single BAA maskalready requires about 4000 DRAM modules each of 16 Mbits for holdingthe expanded dot pattern data of 6-inch wafer. Thus, the system thatuses such a BAA column in plural numbers such as four for the exposureof 12-inch wafer, requires enormous memory capacity and hence a BAAcontrol circuit of enormous size. Such a system is deemed unrealisticand inappropriate for the exposure system used for mass production oflow cost semiconductor devices.

Thus, the object of the present embodiment is to provide a BAA exposuresystem wherein the foregoing problems are effectively eliminated.

More specifically, the present embodiment provides a BAA exposure systemcapable of exposing a pattern on a large diameter substrate withoutincreasing the size of the control system excessively.

Another feature of the present embodiment is to provide a BAA exposuresystem including a plurality of electron optical systems for exposingrespective patterns on respective regions of a common substrate, whereinthe alignment of the patterns exposed by the different electron opticalsystems is achieved exactly.

Thus, the present embodiment provides a charged particle beam exposuresystem for exposing a pattern on an object, comprising:

a base body for accommodating an object to be exposed;

a plurality of electron optical systems provided commonly on said basebody, each of said electron optical systems including:

beam source means for producing a charged particle beam, said beamsource means emitting said charged particle beam toward an object onwhich a pattern is to be exposed, along an optical axis;

beam shaping means for shaping said charged particle beam to produce aplurality of charged particle beam elements in accordance with exposuredata indicative of a dot pattern to be exposed on said object, said beamshaping means comprising a beam shaping mask carrying thereon aplurality of apertures for producing a charged particle beam element byshaping said charged particle beam;

focusing means for focusing said charged particle beam elements upon asurface of said, object;

deflection means for deflecting said charged particle beam elements oversaid surface of said object; and

a column for accommodating said beam source means, said beam shapingmeans, said focusing means, and said deflection means;

said electron optical system thereby exposing said charged particle beamelement upon said object held in said base body;

exposure control system supplied with exposure data indicative of apattern to be exposed on said object and expanding said exposure datainto dot pattern data corresponding to a dot pattern to be exposed onsaid object, said exposure control system being provided commonly tosaid plurality of electron optical systems and including memory meansfor holding said dot pattern data;

said exposure control system supplying said dot pattern data to each ofsaid plurality of electron optical systems simultaneously, such thatsaid pattern is exposed on said object by said plurality of electronoptical systems simultaneously.

According to the foregoing embodiment of the present invention, the sizeof the BAA exposure system is substantially reduced, even when exposinga large diameter wafer by using a plurality of electron optical systemssimultaneously.

FIG. 81 shows the construction of a BAA exposure system 1120 accordingto the present embodiment.

Referring to FIG. 81, the BAA exposure system 1120 includes fourelectron optical systems 1121₁ -1121₄ for exposing a large diameterwafer such as the wafer of 12 inches diameter, wherein each of theelectron optical systems 1121₁ -1121₄ is capable of exposing a substratefor an area corresponding to the 6-inch wafer. The electron opticalsystems 1121₁ -1121₄ are controlled by a single, common main controller1122 of which construction will be described later in detail. The maincontroller 1122 cooperates with an external storage device 1124 thatstores the exposure data, and supplies dot pattern data 1195₁ -1195₄corresponding to the exposure dots to be formed on the substrate, toeach of the electron optical systems 1121₁ -1121₄ for controlling BAAmasks provided therein. It should be noted that each of the electronoptical systems 1121₁ -1121₄ includes an evacuated column 1150₁, whilethe evacuated column 1150₁ accommodates therein an electron gun 1151₁, aBAA mask 52₁, a blanking plate 1153₁ formed with a round aperture, asub-deflector 54₁ and a main-deflector 55₁. Further, the electronoptical systems 1121₁ -1121₄ are provided on a common, hollow base body1140, in which a stage 1143 is provided for holding a wafer 1101 of alarge diameter such as 12 inches. A similar construction of the electronoptical system 1121₁ is provided also on other electron optical systems1121₂ -1121₄.

It should be noted that the BAA mask 1152 produces a plurality ofelectron beam elements simultaneously by shaping an electron beamproduced by the electron gun 1151 similarly to other BAA masks describedbefore, and includes a plurality of deflectors provided incorrespondence to the beam shaping apertures on the BAA mask. Further,the sub-deflector 1154 cooperates with the main deflector 1155 to causethe electron beam elements produced by the BAA mask 1152 to scan overthe surface of the substrate 1160 similarly as before. Further, there isprovided a reflection electron detector 1156 for detecting reflectedelectrons produced as a result of irradiation of the electron beamelements. In FIG. 81, the electron lenses are omitted from illustrationfor the sake of clarity of the drawing.

In the construction of FIG. 81, it should be noted that the dot patterndata 1195₁ -1195₄ produced by the BAA controller 1123 under control ofthe main controller 1122, are supplied to the respective electronoptical systems 1121₁ -1121₄ via corresponding amplifiers 1125₁ -1125₄.Similarly, the main controller 1122 controls the sub-deflectors 54 ofthe electron optical systems 1121₁ -1121₄ via respective amplifiers1126₁ -1126₄ and corresponding variable delay lines 1127₁ -1127₄.Further, the main controller 1122 controls the movable stage 1143 via astage drive circuit 1128.

In the system of FIG. 81, it should be noted that there is provided atiming detection circuit 1129 for detecting the timing of operation ofthe BAA masks 1152, wherein the timing detection circuit 1129 issupplied with output signals from the reflection electron detectors 1156of all of the electron optical systems 1121₁ -1121₄ and controls thevariable delay lines 1127₁ -1127₄ such that the timing of beamdeflection or scanning is aligned for all of the electron opticalsystems 1121₁ -1121₄. Further, there is provided a laser interferometer1144 in the base body 1140 for detecting the position of the movablestage 1143. The output of the laser interferometer 1144 is fed back tothe main controller 1122.

FIG. 82 shows the construction of the base body 1140 on which theelectron optical systems 1121₁ -1121₄ are provided.

Referring to FIG. 82, the base body 1140 defines therein a hermeticallysealed space 1141 in which the foregoing movable stage 1143 of a squareform is provided. The stage 1143 forms, together with a drive mechanismnot illustrated and moving the stage 1143 in the X- and Y-directions, astage assembly 1142.

The stage 1143 is defined by side walls 1143a and 1143b each forming amirror surface, and laser interferometers Y_(A) and Y_(B) are disposedso as to face the mirror surface 1143a for measuring distances Ya₁ andYb₁, wherein the distances Ya₁ and Yb₁ represent the distances, measuredin the Y-direction, between the laser interferometer Y_(A) and themirror surface 1140a and between the laser interferometer Y_(B) and themirror surface 1140a, respectively. Similarly, laser interferometersX_(A) and X_(B) are formed so as to face the mirror surface 1140b formeasuring distances Xb₁ and Xa₁ in the X-direction, respectively. Itshould be noted that the two laser interferometers Y_(A) and Y_(B) haverespective optical axes l₁ and l₂ and are disposed with a mutualseparation of Lx in the X-direction. Similarly, the two laserinterferometers X_(A) and X_(B) have respective optical axes l₃ and l₄and disposed with a mutual separation of Ly in the Y-direction.

Thus, the first electron optical system 1121₁ having an electron beamcolumn 1150₁ is provided on the base body 1140 such that the opticalaxis of the electron optical system 1121₁ coincides with theintersection of the optical axis l₁ of the laser interferometer Y_(A)and the optical axis l₃, wherein the foregoing intersection isrepresented in FIG. 82 by a point P. It should be noted that the point Phas a coordinate (X_(a), Y_(a)) with respect to an origin 1165 set atthe lower left corner of the base body 1140.

On the other hand, the second electron optical system 1121₂ is providedon the base body 1140 generally in correspondence to an intersection ofthe axes l₂ and l₃ represented by a point Q, wherein the electronoptical system 1121₂ has a corresponding electron beam column 1150₂mounted on a movable stage provided on the base body 1140 in opticalalignment with the axis l₃ so as to be movable in the X-direction asindicated by an arrow 1171.

Further, the third electron optical system 1121₃ is mounted upon thebase body 1140 generally in correspondence to the intersection of theaxes l₂ and l₄ represented by a point R, wherein the electron opticalsystem 1121₃ has a corresponding column 1150₃ mounted on a movable stageprovided on the base body 1140 so as to be movable in the X-direction asindicated by an arrow 1175 as well as in the Y-direction as indicated byan arrow 1176. Similarly, the fourth electron optical system 1121₄ ismounted upon the base body 1140 generally in correspondence to theintersection of the axes l₁ and l₄ represented by a point S, wherein theelectron optical system 1121₄ has a corresponding column 1150₄ mountedupon a movable stage provided on the base body 1140 in optical alignmentwith the axis l₁ so as to be movable in the Y-direction as indicated byan arrow 1174.

FIG. 83 shows a detailed construction of the BAA exposure system of FIG.83, wherein only a part of the structure will be shown for the same ofsimplicity.

Referring to FIG. 83, it will be noted that the base body 1140accommodates therein the stage mechanism 1142, wherein the stagemechanism includes the movable stage 1143 carrying thereon the substrate1160 as already noted. The base body 1140 further supports the electronoptical systems 1121₁ -1121₄ on an upper major surface 1140c thereof,wherein only the electron optical systems 1121₁ and 1121₂ areillustrated for the sake of simplicity. It should be noted that theelectron optical system 1121₁ is fixed upon the base body 1140 inoptical alignment with the point P shown in FIG. 84, while the electronoptical system 1121₂ is provided on a movable stage mechanism 1172₂ thatholds the column 1150₂ of the electron optical system 1121₂ movably inthe X-direction. The stage mechanism 1172₂ includes a drive shaft 1172aand a correspondingly guide 1172b and is covered by a flexible seal 1113of bellows.

FIG. 83 shows the control system of the BAA exposure system 1120 indetail, wherein the control system of FIG. 83 is similar to the onedescribed previously in FIG. 3 with reference to the prior art.

More specifically, a CPU 1180, forming a part of the main controller1122, reads out the pattern data to be exposed and supplies the same toa data expansion unit 1191 of the BAA controller 1123 via a buffermemory 1190 also forming a part of the BAA controller 1123, wherein thedata expansion unit 1191 expands the exposure data into dot pattern dataand stores the same in a canvas memory 1192, which is formed of anextensive array of DRAMs. The canvas memory 1192 in turn supplies thedot pattern data to a data rearrange circuit 1193, of which constructionis described in detail in the U.S. patent application Ser. No.08/241,409, op. cit., and the exposure dot data is supplied from thedata rearrange circuit 1193 to a data output circuit 1194 included alsoin the BAA controller 1123 together with the canvas memory 1192 and thedata rearrange circuit 1193, wherein the data output circuit 1194supplies the exposure dot data 1195₁ -1195₄ for the electron opticalsystems 1121₁ -1121₄, respectively via corresponding amplifiers 1125₁-1125₄.

In the construction of the BAA controller 1123 above, it will be notedthat the extensive memory array forming the canvas memory 1192 is usedcommonly by the electron optical systems 1121₁ -1121₄ and the BAAexposure system is constructed with a substantially reduced size andhence cost.

The main controller 1122 includes an exposure controller 1181 thatcontrols the data expansion unit 1191 and the data arranging circuit1193 similarly as the conventional system of FIG. 3. The exposurecontroller 1181 further controls the main and sub-deflectors 1154₁ and1155₁ provided in the electron optical system 1121₁ by way of deflectioncontrollers 1162 and 1163 for causing the electron beam elements, shapedby the BAA mask 1152₁, to scan over the surface of the substrate 1101,wherein the deflection controller 1162 produces the deflection controlsignals 1182₁ -1182₄ respectively in correspondence to the electron beamoptical systems 1121₁ -1121₄ for controlling the sub-deflectors 1154₁-1154₄. In order to adjust the timing of the beam scanning, thedeflection control signals 1182₁ -1182₄ are supplied to thecorresponding sub-deflectors 1154₁ -1154₄ via the delay lines 1127₁-1127₄ as described previously. Thereby, the delay of the delay lines1127₁ -1127₄ is set by detecting the difference in the timing of theturning on and turning off of the electron beam elements in the electronoptical systems 1121₁ -1121₄ by means of the reflection electrondetectors 1156₁ -1156₄.

In order to conduct the exposure of large diameter wafer such as a waferof 12 inches diameter, it should be noted that electron optical systems1121₁ -1121₄ have to be aligned with each other exactly. Hereinafter,the procedure for aligning the electron optical systems will bedescribed with reference to FIG. 84.

Referring to FIG. 84, it will be noted that the surface of the substrate1101 is divided into number of chip areas 1100, wherein the electronoptical system 1121₁ is used for exposing the chips on the lower leftquadrant of the wafer 1101, the electron optical system 1121₂ is usedfor exposing the chips on the lower right quadrant of the wafer 1101,the electron optical system 1121₃ is used for exposing the chips on theupper right quadrant of the wafer 1101, and the electron optical system1121₄ is used for exposing the chips on the upper left quadrant of thewafer 1101. In such a case, it is desired to set the interval betweenthe electron optical systems 1121₁ -1121₄ to be a multiple integer ofthe size of the chip 1100 to be exposed on the substrate 1101, for theefficient use of the substrate 1101. For example, the distance A betweenthe electron optical systems 1121₁ and 1121₄ or 1121₂ and 1121₃ may beset five times as large as the size a of the chip 1100 in theY-direction. Similarly, the distance B between the electron opticalsystem 1121₁ and 1121₂ or 1121₃ and 1121₄ may be set four times as largeas the size b of the chip 1100 in the X-direction.

In order to achieve such an optimization of the electron opticalsystems, the stage mechanisms 1172 that carries the columns of theelectron optical systems 1121₂ -1121₄ are activated such that theelectron optical system 1121₂ is moved, with respect to the referenceoptical system 1121₁, in the X₁ -direction with a distance of Dx.Thereby, the optical system 1121₂ moves from the position Q to a newposition Q₁. Similarly, the electron optical system 1121₃ is moved, fromthe original position R, in the X₁ direction with a distance of Dx₁ andin the Y₁ direction with a distance of Dy₁, to reach a new position R₁.Further, the electron optical system 1121₄ is moved, from the originalposition S, in the Y₁ direction with a distance of Dy, to reach a newposition S₁.

As a result of the shifting of the position of the electron opticalsystems 1121₁ -1121₄, the position of the electron optical systems hasto be corrected in the main controller 1122 for each of the electronoptical systems 1121₁ -1121₄. It should be noted that the laserinterferometers used for detecting the stage position and hence thewafer position cannot be moved together with the electron opticalsystems.

Such a correction is easily achieved by adding the amount of the shaftsuch as Dx and Dy to the original coordinate of the electron opticalsystems as indicated in FIG. 85. For example, the position of theoptical axis of the electron optical system 1121₁ does not change and isgiven as

    X.sub.1 =Xa,

    Y.sub.1 =Ya,

while the position of the optical axis of the electron optical system1121₂ is given as

    X.sub.2 =Xa+Lx+Dx,

    Y.sub.2 =Ya+Ly+Dy.

Further, the position of the optical axis of the electron optical system1121₃ is given as

    X.sub.3 =Xa+Lx+Dx+Dy(Xb-Xa)/Ly,

    Y.sub.3 =Ya+Ly+Dy+Dx(Yb-Ya)/Lx.

The position of the optical axis of the electron optical system 1121₄ isgiven as

    X.sub.4 =Xa+Dy(Xb-Xa)/Ly

    Y.sub.4 =Ya+Ly+Dy.

By employing the construction of the BAA exposure system of the presentembodiment, it is possible to expose a wafer of 12 inches diameter withthe time needed for exposing a wafer of 6 inches diameter. It should benoted that each of the electron optical systems 1121₁ -1121₄ exposesonly one-quarter of the 12 inches wafer, and it is possible to obtain athroughput of about 30 wafers per hour.

When exposing semiconductor devices having a different size for theedges a and b, the setting of the electron optical systems 1121₁ -1121₄is changed, and the exposure is conducted similarly. Typically, the X-Ystage mechanism 1172 can cover a range of ±15 mm. Thus, the BAA exposuresystem of the present embodiment can expose the integrated circuit chipsof various sizes.

[ninth embodiment]

In the conventional BAA exposure system described heretofore such as theone described with reference to FIG. 3, the objective lens 107 isprovided above the substrate 115 and there has been no substantialleakage of the magnetic field of the electron lens 107 to the substrate115.

On the other hand, there is a different type of electron lens calledimmersion lens that is promising for the objective lens 107 of the BAAexposure system. In immersion lenses, an object or substrate is placedwithin the magnetic field created by the lens, and the focusing of theelectron beam is achieved in such a magnetic field. The immersion lensis advantageous for the BAA exposure system in the point that it causeslittle aberration in the electron beam.

Meanwhile, most of the conventional electron beam exposure systems,including the BAA exposure systems described heretofore, carry out theexposure of patterns while moving the substrate continuously, forimproved throughput of exposure. Thus, use of the foregoing immersionelectron lens in combination with such a conventional electron beamexposure systems is thought a promising approach for realizing highresolution and high throughput electron beam exposure systems.

However, such a combination of the immersion lens and the electron beamexposure system causes a problem in that an eddy current is induced in aconductor layer or pattern formed on the substrate as the substrate ismoved continuously through the magnetic field created by the immersionlens. As such an eddy current produces a magnetic field, thereinevitably occurs a deviation in the beam position as compared with theintended beam position.

FIG. 86 shows a conventional immersion lens 1250 in an enlarged scale.

Referring to FIG. 86, the immersion lens 1250 is formed of a firstobjective lens 1252 and a second objective lens 1254, in which the lens1252 is provided in the upstream side of the lens 1254. Further, asubstrate 1256 is disposed between the lens 1252 and the lens 54. InFIG. 86, it is assumed that the substrate 1256 is moved in the directionto the right as indicated by an arrow by means of a drive mechanism notillustrated.

It should be noted that the substrate 1256 carries thereon a number ofconductor patterns and/or semiconductor elements that form a conductivepart. Thus, the magnetic field created between the two opposing lenses1252 and 1254 inevitably interlines with the substrate 1256, and an eddycurrent flows as the substrate 1254 moves in the direction shown in thearrow. It should be noted that such a motion of the conductive part inthe magnetic field induces a voltage v represented as V=-dφ/dt, whereinφ represents the magnetic flux, and the voltage thus induced causes theforegoing eddy current.

The eddy current flows through the substrate 1256 in the direction so asto oppose the magnetic field created by the lenses 1252 and 1254.Assuming that the magnetic flux caused by the lenses 1252 and 1254 isdirected in the upward direction, an eddy current I_(eddy-A) flows in aregion A of the substrate 1256 in a clockwise direction when viewed fromthe upward direction of the substrate 1256, so as to oppose theincreasing magnetic flux. It should be noted that the region A is theregion that is entering the magnetic field created by the lenses 1252and 1254 and experiences an increase in the magnetic field. On the otherhand, in a region B of the substrate 1256 that is exiting from the lensmagnetic field, the eddy current flows in a counter clockwise directionas viewed from the upward direction of the substrate 1256 as indicatedby a current I_(eddy-B), so as to prevent the decrease of the magneticflux.

As a result of the eddy currents I_(eddy-A) and I_(eddy-B) thus induced,there is formed a magnetic flux B_(eddy) as indicated in FIG. 86,wherein the magnetic flux B_(eddy) thus created crosses the electronbeam 1268 and causes a deviation H as indicated in the beam position.

Thus, conventional electron beam exposure system that uses the immersionlens has corrected the beam deviation H by disposing hole sensors 1258and 1260 in the area where the eddy magnetic flux B_(eddy) is expectedas indicated in FIG. 87. Thus, the beam correction is achieved byevaluating the beam deviation H by a control unit 1266 based upon theoutput of the hole sensors 1258 and 1260 and by providing acounter-acting beam deflection to the electron beam 1268 by energizingan electrostatic deflector 1262. It should be noted that the holesensors 1258 and 1260 are fixed against the body of the electron beamexposure system. As the magnetic field of the lens is set constant, itis possible to evaluate the magnetic field B_(eddy) in terms ofdeviation of the magnetic field strength.

In such a construction, however, exact detection of the magnetic fieldof the eddy current by means of the hole sensors 1259 and 1260 isdifficult, as the magnitude of such an eddy magnetic field is verysmall, less than 1 mGauss. Further, it is difficult to mount the tinyhole sensors 1258 and 1260 upon the electron optical system of theexposure system with necessary precision.

In addition, such a construction has another drawback in the point thata magnetic field B_(coil) created by the electromagnetic deflector 1264,which are used in the electron beam exposure systems for deflecting theelectron beam over the surface of the substrate 11256, may provideunwanted interference upon the hole sensors 1258 and 1260 as indicted inFIG. 88. When such a jamming is caused by the electromagneticdeflectors, the desired correction of the beam position is no longerpossible. Further the construction of FIG. 87 is disadvantageous in viewof complexity Of the electron optical system that requires a number ofhole elements to be provided in the vicinity of the area of exposure.

Thus, the object of the present embodiment is to provide a chargedparticle beam exposure system that uses an immersion electron lens,wherein the compensation of beam offset caused by the eddy current issuccessfully achieved with a simple construction of the electron opticalsystem.

More specifically, the present embodiment provides a charged particlebeam exposure system for exposing a pattern on an object by a chargedparticle beam, comprising:

a stage for holding an object movably;

beam source means for producing a charged particle beam and emittingsaid charged particle beam toward said object held on said stage alongan optical axis; and

a lens system for focusing said charged particle beam upon said objectheld on said stage;

said lens system including an immersion lens system comprising: a firstelectron lens disposed at a first side of said object closer to saidbeam source means, a second electron lens disposed at a second, oppositeside of said object, said first and second electron lenses creatingtogether an axially distributed magnetic field penetrating through saidobject from said first side to said second side, and a shield plate of amagnetically permeable conductive material disposed between said objectand said first electron lens, said shield plate having a circularcentral opening in correspondence to said optical axis of said chargedparticle beam.

According to the present embodiment as set forth above, the electricfield inducted as a result of the eddy current is successfully capturedby the magnetic shield plate and guided therealong while avoiding theregion in which the electron beam passes through. Thereby, adversaryeffects upon the electron beam by the eddy current is effectivelyeliminated.

First, the overall construction of an electron beam exposure system 1201according to the present embodiment will be described with reference toFIG. 89.

Referring to FIG. 89, the electron beam exposure system 1201 includes anelectron gun 1202 for emitting an electron beam toward a substrate 1226held on a movable stage 1224, along an optical axis 1203. The electronbeam thus emitted is then focused upon the substrate 1226 by means ofelectron lenses 1204, 1206, 1208, 1210, 1212 and 1214, wherein theforegoing electron lenses have respective intensities controlled by acontrol system omitted from illustration. Further, the electron beamexposure system 1201 includes a beam shaping mask 1218 for shaping theelectron beam emitted from the electron gun 1202 to have a predeterminedshape such a a rectangular shape, and another beam shaping mask 1220 forshaping the electron beam already shaped by the mask 1218 to have apredetermined beam shape to be exposed on the substrate 1226.Furthermore, in order to turn on and turn off the electron beam on thesubstrate 1226, a blanking plate having a round aperture 1222 isprovided. When the electron beam is deflected away from the roundaperture 1222, the electron beam is turned off from the surface of thesubstrate 1226.

FIG. 89 further shows a cross over image corresponding to the electronbeam as emitted by the electron gun 1202 by a broken line and a shapedimage corresponding to the image of the beam shaping mask 1218 by acontinuous line. The intensity of the respective electron lenses isindicated in FIG. 89 by a hatching. Thus, it will be noted that theforegoing shaped image is focused upon the surface of the substrate1226, after further being shaped by the beam shaping mask 1220, by theelectron lenses 1204, 1206, 1208, 1210, 1212 and 1214 forming together ademagnifying electron optical system. Thereby, the lenses 1212 and 1214form together an immersion lens 1216 acting as an objective lens.

Hereinafter, the construction of the immersion lens 1216 formed by theforegoing electron lenses 1212 and 1214 will be described with referenceto FIG. 90.

Referring to FIG. 90, the immersion lens 1216 is formed of the firstelectron lens 1212 and the second electron lens 1214 disposed so as toface with each other across the substrate 1226, wherein the lens 1212 isdisposed in the upstream side of the substrate 1226 while the lens 1214is disposed in the downstream side thereof. Thereby, the lenses 1212 and1214 form a magnetic field in the vicinity of the surface of thesubstrate 1226, wherein the magnetic field thus induced focuses theelectron beam emitted from the electron gun 1202 upon the surface of thesubstrate 1226. As already noted, the immersion lens having such aconstruction has an advantageous feature of very small aberrations ascompared with conventional electron lenses.

FIG. 91 shows the magnetic field induced in the immersion lens 1216 bythe electron lenses 1212 and 1214. It will be noted that the lenses 1212and 1214 create respective magnetic fields 1212B and 1214B acting in theupward direction, of which intensities are represented by respectivehatchings. Further, there is formed a synthetic magnetic field 1216B asa sum of the magnetic fields 1212B and 1214B.

In the immersion lens 1216 of FIG. 90, it should be noted that there isprovided a shield plate 1230 of a magnetically permeable conductor,wherein the shield plate 1230 has a central opening 1232 incorrespondence to the passage of the electron beam and is disposedbetween the upper lens 1212 and the substrate 1226. Typically, theshield plate 1230 is formed of permalloy. Although not illustrated inFIG. 90, the shield plate 1230 is fixed in the electron optical systemof the exposure system 1201 such that the plate 12030 does not move evenwhen the substrate 1226 is moved by the stage 1224. Thus, no eddycurrent occurs even when the substrate 1226 is moved in the magneticfield created by the electron lenses 1212 and 1214.

Next, the principle of the present embodiment will be described withreference to FIG. 92. Similarly as before, it is assumed that thesubstrate 1226 is moving to the right in the direction of arrow whileinterlining with the synthetic magnetic flux of the lens 1216 thatcorresponds to the magnetic field 1216B.

Referring to FIG. 92, it will be noted that there is induced an eddycurrent I_(eddy-A) in the substrate 1226 in correspondence to the regionA in which the interlining magnetic flux is increasing, wherein the eddycurrent I_(eddy-A) flows in the clockwise direction in the vicinity ofthe region A. On the other hand, in the vicinity of the region B wherethe interlining magnetic flux of the immersion lens 1216 is decreasing,the eddy current flows in the counter clockwise direction as indicatedby a current I_(eddy-B).

Thus, there is formed more or less constantly a magnetic field B_(eddy)as a result of the magnetic fields associated with the respective eddycurrents I_(eddy-A) and I_(eddy-B), although the magnitude of themagnetic field B_(eddy) may change depending upon the speed of movementof the substrate 1226. It should be noted that the regions A and B aredetermined with respect to the magnetic field 1216B of the immersionlens and are more or less stationary even when the substrate 1226 ismoved by the stage 1224.

In the present embodiment, most of the eddy magnetic field B_(eddy) thusinduced is captured by the permeable shield plate 1230 disposed abovethe substrate 1226 and is guided therealong. Thereby, the magnetic fieldB_(eddy) positively avoids the aperture 1232 provided in the shieldplate 1230 as the electron beam passage, and the electron beam passingthrough the aperture 1232 experiences little influence by such eddymagnetic field 1216B.

In the exposure of actual semiconductor substrate that may include acomplex conductor pattern, the eddy current induced therein mayfluctuate with time and create a high frequency magnetic field. As sucha high frequency magnetic field not only passes through the shield plate1230 but induces an eddy current in the shield plate 1230 itself, it isnecessary to evaluate the effect of such a high frequency magnetic fieldinduced by the eddy current I_(eddy-A) and I_(eddy-B).

FIG. 93 shows such a case in which the high frequency magnetic fieldsB_(eddy-A) and B_(eddy-B) induce corresponding high frequency eddycurrents I'_(eddy-A) and I'_(eddy-B) in the shield plate 1230, whereinthe eddy currents I'_(eddy-A) and I'_(eddy-B) act to oppose the magneticfields B_(eddy-A) and B_(eddy-B). In such a case, the energy of the highfrequency magnetic fields B_(eddy-A) and B_(eddy-B) is absorbed by theshield plate 1230 as a result of induction of the corresponding eddycurrents I'_(eddy-A) and I'_(eddy-B). Thus, the shield plate 1230 isalso effective for eliminating the unwanted magnetic field from thepassage region 1232 of the electron beam even in such a case.

Next, the shape of the shield plate 1230 will be considered withreference to FIGS. 94 and 96.

In the shield plate 1230 for use in the electron optical system of theelectron beam exposure system, it is necessary that the shield plate1230 has a symmetricity about the electron beam path. Thus, the centralopening 1232 of the shield plate 1230 should have a circular shape.Further, the central opening 1232 should have a sufficient size forallowing the reflected electrons to pass therethrough and reach adetector 1237 provided above the shield plate 1230 as indicated in FIG.95. Further, it should be noted that excessively small central aperture1232 may invite unwanted deposition of C on the shield plate 1230 asindicated in FIG. 95 by a hatched region, while such a deposition of Ctends to invite a problem of charge up that causes an unwanteddeflection of the electron beam.

FIG. 94 shows the intensity profile of the magnetic field 1216B of theimmersion lens 1216 taken along the plane of the substrate 1226.

Referring to FIG. 94, it should be noted that there exist regions A andB wherein the change of the magnetic field 1216B is steep. The regions Aand B actually form an annular region defined by an outer diameter ofφ_(Dmax) and an inner diameter of φ_(Dmin), wherein the foregoingregions A and B are mostly responsible for the formation of the eddycurrent in the substrate 1226.

Thus, in order to intercept the magnetic field B_(eddy) efficiently bythe shield plate 1230, it is necessary to form the shield plate 1230such that the shield plate 1230 has an inner diameter a smaller than theforegoing inner diameter φ_(Dmin) and an outer diameter smaller than theforegoing outer diameter φ_(Dmax) as indicated in FIG. 96.

With such an optimization of the shield plate 1230 with respect to theinner diameter a and an outer diameter b, one obtains a structure shownin FIG. 97A which corresponds to the structure of FIG. 95, wherein, inthe structure of FIG. 97A, it will be noted that the exit angle of thereflected electron beam through the central opening 1232 is limited toθ₁ by the upper rim or edge of the opening 1232. Associated with this,there occurs a substantial deposition on the lower major surface of theshield plate 1230 as well as on the inner wall of the opening 1232. Itshould be noted that the deposition of C on the inner wall of theopening 1232 is most harmful in the electron beam alignment.

In order to improve the foregoing problems, the present embodimentprovides a taper on the upper major surface of the shield plate 1230 incorrespondence to the central opening 1232, such that the exit angle ofthe reflection electrons increases from θ₁ to θ₂. Thereby, the problemof carbon deposition on the inner wall of the central opening 1232 isalso eliminated.

It should be noted that the electron optical system that uses theimmersion lens of the present embodiment is applicable to the BAAexposure system described heretofore with various embodiments as well asto a block exposure system such as the one described in the U.S. Pat.Nos. 5,051,556 and 5,173,582, which are incorporated herein asreference.

[tenth embodiment]

In the BAA exposure system described heretofore, the desired pattern isexposed on a substrate in the form of aggregation of exposure dots. Byturning on and turning off the exposure dots by controlling the BAA maskin response to dot pattern data, it is possible to expose versatilesemiconductor patterns as in the case of microprocessors. On the otherhand, there frequently occurs a need to expose a semiconductor patternhaving both irregular patterns and regularly repeated patterns, as inthe case of forming a memory together with a microprocessor.

Conventionally, exposure of such a regularly repeated patterns isadvantageously conducted by the so-called block exposure process,wherein the block exposure process decomposes the pattern to be exposedinto limited numbers of fundamental patterns. By shaping an electronbeam by a so-called block mask that carries thereon such fundamentalpatterns in the form of stencil pattern, it is possible to expose thedesired pattern with high efficiency and high resolution. In the blockexposure process, it is possible to expose a pattern having a line widthof 0.1 μm with reliability. About the block exposure process, referenceshould be made to the U.S. Pat. Nos. 5,051,556 and 5,173,582, op cit.

On the other hand, the block exposure system has a drawback in that thepattern that can be exposed is limited to a small number of thefundamental patterns on the block mask or their combinations. In orderto expose versatile patterns by means of the block exposure system, itis necessary to replace the block mask with another one, while such aprocess is cumbersome and decreases the throughput.

Thus, it is thought promising to construct an electron beam exposuresystem that is capable of exposing a pattern both in the BAA exposureprocess that uses a BAA mask and in the block exposure process that usesa block mask.

Accordingly, the present embodiment has an object to provide a chargedbeam exposure process capable of exposing both a BAA exposure processand a block exposure process on a common substrate.

More specifically, the present embodiment provides a charged particlebeam exposure system for exposing a pattern on an object, comprising:

a stage for holding an object thereon;

beam source means for producing a charged particle beam such that saidcharged particle beam is emitted toward said object on said stage alonga predetermined optical axis;

a blanking aperture array provided in the vicinity of said optical axisfor shaping an electron beam incident thereto, said blanking aperturearray including a mask substrate, a plurality of apertures of identicalsize and shape disposed in rows and columns on said mask substrate and aplurality of deflectors each provided in correspondence to an apertureon said mask substrate;

a block mask provided in the vicinity of said optical axis, said blockmask carrying thereon a plurality of beam shaping apertures of differentshapes for shaping an electron beam incident thereto;

selection means for selectively deflecting said electron beam from saidbeam source means to one of said blanking aperture array and said blockmask;

focusing means for focusing an electron beam shaped by any of saidblanking aperture array and said block mask upon said object on saidstage.

According to the construction of the present embodiment set forth above,it is possible to switch the MAA exposure and block exposure by usingthe single electron exposure system. Thereby, the addressing deflector,used in the block exposure process for selecting an aperture on theblock mask, is used also as the selection beams for selecting the BAAexposure process and the block exposure process. Thereby, no extraneousfixture is needed for implementing the selection of the exposure mode.

FIG. 98 shows the principle of the present invention schematically.

Referring to FIG. 98 showing an electron beam exposure system 1310according to the present embodiment, the electron beam exposure system1310 includes selection means 1313, supplied with selection data 1316from an external control system as a part of exposure data 1315, forselecting one of a BAA mask 1311 and a block mask 1312 for shaping anelectron beam 1314 produced by an electron gun not illustrated. The BAAmask 1311 carries thereon a number of apertures of the same size andshape as well as corresponding deflectors, in a row and column formationfor shaping the electron beam 1314 into a number of electron beamelements forming collectively an electron beam bundle. Thus, byselecting the BAA mask 1311, the electron beam 1314 hits the BAA mask1311 as indicated by an arrow 13114₁, and the exposure of the electronbeam bundle formed as a result of beam shaping in the BAA mask 1311, ismade upon the surface of the substrate as a pattern 1317. Similarly, byselecting the BAA chip 1311 that carries thereof fundamental patterns ofthe pattern to be exposed, the electron beam 1314 hits the blanking mask1312 and a pattern 1318 is exposed on the same substrate as indicated inFIG. 98.

FIG. 99 shows the construction of an electron beam exposure system 1320according to the present embodiment in detail.

Referring to FIG. 99, the electron beam exposure system 1320 includes anelectron optical system 1310 corresponding to the system of FIG. 98 anda control system 1321 for controlling the electron optical system 1321.

The electron optical system 1310 has a construction similar to the onedescribed already with reference to FIG. 3 and includes an electron beamcolumn that accommodates therein an electron gun 1323 for emitting anelectron beam toward a substrate 1330 held on a movable stage 1329, anaddressing deflector 1324 to be described later in detail, a beamshaping mask assembly including a BAA mask 1311 and a block mask 1312, ablanking deflector 1325 and a corresponding blanking plate 1326 forselectively turning off the electron beam or electron beam element onthe surface of the substrate 1330, and various electron lenses forfocusing the electron beam upon the surface of the substrate 1330 withdemagnification. Further, main and sub-deflectors 1327 and 1328 areprovided in the vicinity of the substrate 1330 for moving the electronbeam over the surface of the substrate 1330.

In FIG. 99, it should further be noted that the electron beam exposuresystem includes a CPU 1381 and a data storage device 1350 such as amagnetic disk device or a magnetic tape device, wherein the devices 1350is used to store pattern data corresponding to a device pattern of asemiconductor device to be written on a substrate. The CPU 1351 and themagnetic disk device 1352 are connected commonly to a system bus 1350a,and the CPU 1351 reads out the pattern data from the magnetic disk 1352via the system bus 1350a. The pattern data thus read out on the systembus 1350a is then transferred via an interface circuit 1352 to a datamemory unit 1353 and simultaneously to a stage controller 1354A.

The electron beam exposure system further includes an evacuated column1322 as usual, and there is provided an electron gun 1323 at the toppart of the column 1322 for producing an electron beam. The electronbeam thus produced by the electron gun 1323 is focused on a substrate1330 that is held on a movable stage 1329 after passing through variouselectron lenses 1321A, 1321B, 1321C, 1321D and 1321E as well as afterbeing deflected by an addressing deflector assembly 1324 to be describedlater in detail and a blanking deflector 1325, wherein the electron lens1321E acts as the objective lens for focusing the electron beam on thesurface of the substrate 1330. The deflector 1325 is used for a blankingcontrol together with the electron lens 1321C and a blanking apertureprovided in a blanking plate 1326, and controls the turning-on andturning-off of the electron beam on the substrate 1330. The electronlens 1321B on the other hand is used in combination with the addressingdeflector assembly 1324 and a beam shaping masks 1311 and 1312 forshaping the electron beam into a desired beam shape.

The electron beam thus shaped is deflected by the electrostaticsub-deflector 1328 and is moved over the surface of the substrate 1330when focused thereon by the electron lens 1321E. Further, there isprovided an electromagnetic main deflector 1327 for deflecting thefocused electron beam over a wide range of the substrate surface. Itshould be noted that the electrostatic deflector 1328 provides thedeflection of the electron beam over a limited area that is smaller thanabout 100 μm×100 μm, with a high speed of about 0.6 μs/3 μm. On theother hand, the electromagnetic deflector 1327 provides the deflectionover a large area as large as 1 mm×1 mm though with a limited speed ofabout 2-30 μs/100 μm.

In operation, the pattern data stored in the data memory unit 1353 isread out by an exposure controller 1354. The pattern data thus producedis then supplied to a blanking control circuit 1368 that extracts ablanking control signal from the pattern data and supplies the same tothe electrostatic deflector 1325 via a D/A converter 1367.Simultaneously, the exposure controller 1354 produces beam shape controldata specifying the beam shape that is to be used in the block exposureprocess.

It should be noted that the beam shape control data is producedconsecutively in correspondence to the shot and are supplied to theaddressing electrostatic deflector assembly 1324 after a conversion toan analog signal in a D/A converter 1360. More specifically, theexposure controller 1354 produces deflection control data incorrespondence to each shot by referring to a deflection data memory 55that stores the energization to be applied to the deflector assembly1324 as a function of the deflection data, and supplies the energizationthus read out to the electrostatic deflector assembly 1324. Further, thepattern exposure controller 1354 produces other deflection control datafor the main and sub-deflectors and supplies the same to the maindeflector 1327 as well as to the sub-deflector 1328 after a conversionto an analog signal in respective D/A converters 1361 and 1362. Further,the sub-deflector 1328 is controlled in response to the movement of thestage 1329 and hence the substrate 1330 by the sequence controller 1354Athat controls the sub-deflector 1328 via a positional detection circuit1354a that supplies digital output to the D/A converter 1362. Thesequence controller 1354A further controls the stage 1329 via a stagedrive mechanism 1329A while monitoring the stage position by a laserinterferometer 1329B.

Thus, in the block exposure mode, the electron beam is shaped by aselected aperture on the block mask 1321 in response to the addressingcontrol data supplied from the exposure controller 1354 to theaddressing deflector assembly 1324 and is exposed on the surface of thesubstrate 1330 as usual in the block exposure process.

In the BAA exposure mode, on the other hand, the exposure data issupplied from the interface circuit 1352 to a buffer memory 1356₁forming a part of a data expansion circuit 1386₁, wherein the exposuredata held in the buffer memory 1356₁ is supplied to a data expansionunit 1386₂, included also in the data expansion circuit 1386₁, forexpansion into dot pattern data corresponding to the bitmap of theexposure pattern. The dot pattern data thus obtained is held in a canvasmemory 1356₃.

The dot pattern data in the canvas memory 1356₃ is read out by a dataarrangement circuit 1356₄ and is supplied to a plurality of data outputcircuits 1357 provided in correspondence to a plurality of apertures onthe BAA mask 1311, wherein the data output circuits 1357 controls thedeflectors on the BAA mask 1311 via corresponding driver circuits 1358.Thus, the construction of the circuits 1356₁ -1356₄ as well as theconstruction of the circuits 1387 and 1358 are known from theconventional example such as the one described already with reference toFIG. 100.

FIG. 100 shows the construction of the beam shaping masks 1311 and 1312as well as cooperating electrostatic deflector assembly 1324 in detail.

Referring to FIG. 100, the deflector assembly includes electrostaticdeflectors 1324₁ -1324₄, wherein the deflector 1324₁ deflects theelectron beam 1314 away from an optical axis 1339 set so as to passthrough the round aperture on the blanking plate 1326, while thedeflector 1324₂ deflects back the electron optical beam 1314₁ or 1314₂thus deflected, such that the electron beam passes through a pathparallel to but offset from the optical axis 1339. Thereby, the electronbeam hits, if deflected as indicated by the beam 1314₁, the BAA mask1311 perpendicularly and experiences a beam shaping according to theapertures formed on the BAA mask 1311. After passing through the mask1311, the electron beam is deflected by the deflector 1324₃ toward theoptical axis and is further deflected by the deflector 1324₄ such thatthe electron beam travels along a path coincident to the optical axis1339.

On the other hand, in the block exposure mode, the electron beam 1314 isdeflected by the deflector 1324₁ as indicated by the beam 1314₂, whereinthe electron beam 1314₂ is deflected further by the deflector 1324₂ andhits the block mask 1312 perpendicularly. Upon passage through the blockmask 1312, the beam 1314₂ experiences a beam shaping according to theselected aperture, and the electron beam thus shaped is deflected towardthe optical axis 1339 by the deflector 1324₃ and further by thedeflector 1324₄, wherein the electron beam travels along a path, afterdeflection by the deflector 1324₄, which is coincident to the opticalaxis 1339.

In the construction of FIG. 100, it will be noted that the BAA mask 1311is fixed inside the column 1322 of the electron optical system while theblock mask 1312 is held movable for allowing replacement of the blockmask. For this purpose, the block mask 1312 is held on a movable stage1332 that retracts the mask 1312 into a sub-chamber 1331 formed on theelectron beam column 1322 when replacing the mask 1312.

Further, in order to prevent the leakage of the electron beam at a gapformed between the fixed BAA mask 1311 and the movable blanking mask1312, there is provided a shielding member 1333 below the mask 1312 forinterrupting the leakage electron beam.

FIG. 101 shows the construction of the BAA mask 1311 and the block mask1312.

Referring to FIG. 101, the BAA mask 1311 carries a blanking aperturearray 1334 on a central part thereof as usual, while the block mask 1312carries a plurality of block patterns 1335-1338 each of different shape.Further, the masks 1311 and 1312 have rectangular openings 1420-1423 and1425-1428 at respective corners. Thereby, the electron beam 1314₁ has arectangular shape as indicated in FIG. 101, while the electron beam 14₂have a similar rectangular shape and addresses one 13of the blockpatterns 1335-1338 as indicated by numerals 1314₂₋₂, 1314₂₋₃ and1314₂₋₄.

It should be noted that the masks 1311 and 1312 are disposed in thecolumn of the electron beam exposure system such that the optical axis1339 passes through the boundary between the masks 1311 and 1312.Further, it will be noted that the blanking aperture array 1334 isdisposed at a central part of the mask 1311 offset from the optical axis1339 in the X-direction by a distance L₂. Similarly, the center of themask 1312 is offset from the optical axis in the -X direction by adistance L₁, while the distance L₁ is equal to the distance L₂.

FIG. 102 shows the construction of the exposure controller 1354, whereinthe controller 1354 includes a control unit 1354₁ cooperating with thedata memory 1353. In the present embodiment, the data memory 1353 storesexposure data 15 such as data 1315₁ and 1315₂, wherein each of theexposure data 1315₁ and 1315₂ in the data memory 1353 includes a firstdata block 1316 for holding single bit data indicative of whether theexposure data is the data for the BAA exposure process or the blockexposure process. Further, the data 1315₁ for the BAA exposure processincludes a second data block 1370 containing an identification number ofa scanning band in the sub-field by the sub-deflector, and a third datablock 1371a containing pattern data to be exposed in the form bitmapdata. On the other hand, the data 1315₂ for the block exposure processincludes the same second data block 1370 and a third data block 1371b,wherein the third data block 1371b contains the code number of thepattern attached to the patterns 1314₂ -1314₄ as indicated in FIG. 101.Further, in any of the data 1315₁ -1315₂, it should be noted that thereare blocks 1372-1375 for storing the deflection data Xm and Ym for themain deflector 1327 and the deflection data Xs and Ys for thesub-deflector 1328.

The control unit 1354₁ includes a discrimination unit 1354₁₋₁ fordiscriminating the content of the data block 1316. Thus, when thecontent of the data block 1316 is set "1," indicative of the BAAexposure, the control unit 1354₁ supplies the data of the block 1370indicative of the identification number of the sub-scan band of thesub-field, to a register 1354₂, while the register 1354₂ supplies anoutput to the data output circuit 1357. Further, the control unit 13154₁transfers the content of the data block 1371a to a addressing register1354₄ so as to drive the deflector assembly 1324 based upon thedeflection data stored in a BAA deflection memory 1354₃, which forms apart of the exposure controller 1354, provided that the data block 1316contains data "1." Thereby, the content of the data blocks 1372-1375 aresupplied respectively to an Xm register 54₅, a Ym register 1354₆, an Xsregister 11354₇ and a Ys register 1354₈, wherein the registers 1354.sub.5 and 1354₆ drives the main deflector 1361, while the registers 1354₇and 1354₈ drives the sub-deflector 1362 by referring to the content of amemory 1354₉ that stores the energization of the sub-deflector 1362 as afunction of the deflection data. As a result of energization of thedeflectors 1324₁ -1324₄, the electron beam 1314₁ selects the blankingaperture array 1334 formed on the BAA mask 1311 as indicated in FIG.101.

In the event the content of the data field 1316 is "0," on the otherhand, the control unit 1354₁ reads out the content of the memory 1358for a given pattern code held in the data block 1371b, and transfers theenergization data thus read out to the addressing register 1354₃.Thereby, the electron beam 1314₂ is deflected to a selected blockaperture on the mask 1312 such as the aperture 1314₂₋₂ bearing thepattern code "2."

FIGS. 103A-103C show the scanning caused on the substrate 1330 by theelectron beam exposure system of FIG. 99.

Referring to FIG. 103A showing the scanning of a sub-field 1381 by anelectron beam bundle 1385 formed by the BAA mask 1311, the scanning isachieved along a path 1382 by energizing the sub-deflector 1362, whereineach path defines a band. The sub-field 1381 of FIG. 103B, on the otherhand, forms another band formed of a number of such sub-fields 1381₁-1381₁₃ in a main-deflection field 1380 covered by the main deflector1861, wherein the scanning is achieved along a zig-zag path 1883.Further, the main deflection field 1380 of FIG. 103B forms a band 1384on a wafer as indicated in FIG. 103C, wherein the surface of the wafer1330 is divided into a number of chips 1386.

In the present embodiment, it should be noted that the foregoingscanning of the wafer occurs similarly in the BAA exposure mode and inthe block exposure mode as indicated in FIGS. 104A and 104B, whereinFIG. 104A shows examples of exposure data 1315₉₁ -1315₉₅ and FIG. 104Bshows the corresponding pattern formed on a sub-field 1381₇ of the waferor substrate.

Referring to FIG. 104A, the exposure data 1315₉₁ for the sub-scan band1391 of the BAA exposure mode includes the digit "1" in the data block1316 and digit "91" indicative of the sub-scan band in the data block1370. As a result of the exposure, patterns 1400, 1401 and 1402 areexposed. Similarly, the exposure data 1315₉₂ corresponds to the sub-scanband 1392 and exposes the patterns 1403 and 1404 in the BAA exposuremode. The exposure data 1315₉₃ exposes a pattern 1405 similarly in thesub-scan band 1393.

On the other hand, the exposure data 1315₉₄ corresponds to a sub-scanband 1394 and exposes a pattern 1406 designated in the data block 1371baccording to the block exposure process. Similarly, the exposure data1315₉₅ corresponds to a sub-scan band 1395 and exposes a pattern 1407designated in the data block 1371b according to the block exposureprocess.

FIG. 105 shows the exposure operation of the present embodimentconducted in the exposure controller 1354 in the form of a flowchart.

Referring to FIG. 105, the exposure data is read out from the datamemory 1353 in a step S1, wherein a discrimination is made in a step S2about the first data block in a step S2, whether the exposure is to bemade in the BAA exposure mode or in the block exposure mode. If the BAAexposure mode is selected, the memory 1354₃ for the BAA deflection datamemory is referred to in a step S3, and the addressing register 1354₄ isdriven in a step S4. Further, in a step S5, the dot pattern data for theselected sub-deflection band is obtained by conducting a data expansionin the data expansion circuit 1356. Further, the scanning of thesub-deflector 1368 is carried out by reading the content of thesub-deflector memory 1354₉ in a step S6.

When the exposure is to be achieved in the block exposure mode, on theother hand, a step S7 is conducted wherein the memory 1355 is referredto for the necessary deflection of the addressing deflector 1324, and astep S8 is conducted subsequently wherein the addressing register 1354₄is driven with the output of the addressing deflector 1324. Further, astep S9 is conducted wherein deenergization of the blanking deflector1325 is made for carrying out a shot.

Further, there can be various schemes for conducting the exposure asindicated in FIGS. 106A-1406C, wherein FIG. 1406A indicates that each ofthe sub-fields 1381₉ -1381₇ includes both the BAA and block patterns.

In the scheme of FIG. 106B, the exposure is made one sub-deflection bandby one sub-deflection band consecutively from a band 1381₉ to a band1381₈, and from the band 1381₈ to a band 1381₇, wherein both the BAAexposure and block exposure are carried out in each of the bands. Thus,the scheme of FIG. 106B corresponds to the exposure scheme of FIGS. 104Aand 104B.

In the scheme of FIG. 106C, on the other hand, the BAA patterns areexposed preferentially for all of the sub-fields 1381₇ -1381₉, followedby the exposure of the block patterns for all of the sub-fields 1381₇-1381₉.

Further, the present invention is not limited to the embodimentsdescribed heretofore, but various variations and modifications may bemade without departing from the scope of the invention.

What is claimed is:
 1. A method for exposing a pattern on an object bymeans of a plurality of charged particle beams in the form of dotpattern data, said plurality of charged particle beams being producedsimultaneously as a result of shaping of a single charged particle beam,said method comprising the steps of:creating dot pattern data indicativeof said dot pattern data to be exposed; storing said dot pattern data ina first storage device having a first access speed; transferring saiddot pattern data from said first storage device to a second storagedevice having a second, higher access speed; reading said dot patterndata out from said second storage device; and producing said pluralityof charged particle beams in response to said dot pattern data read outfrom said second storage device by means of a blanking aperture array,said blanking aperture array including a plurality of apertures thereineach causing turning-on and turning-off of a changed particle beampertinent to said aperture in response to said dot pattern data.
 2. Amethod as claimed in claim 1, wherein said second storage deviceincludes a plurality of memory devices for storing said dot patterndata.
 3. A method as claimed in claim 2, wherein said step of producingthe plurality of charged particle beams includes a step of transferringsaid dot pattern data via a plurality of channels, such that the samedot pattern data is supplied, in each of said plurality of channels, toa plurality of beam shaping apertures provided on said blanking aperturearray.
 4. A method as claimed in claim 3, wherein said plurality ofmemory devices are arranged to form a plurality of pairs in each of saidplurality of channels,wherein said step of transferring the dot patterndata is conducted, in each of said plurality of channels, to saidplurality of memory pairs, such that, in each of said plurality ofmemory pairs, the dot pattern data is stored in a first memory formingsaid memory pair, and wherein said step of reading said dot pattern datais made, in each of said plurality of channels and in each of saidplurality of memory pairs, such that said dot pattern data is read outfrom a second memory forming said memory pair, while said step oftransferring the dot pattern data is in progress to said first memory.5. A method as claimed in claim 2, wherein said step of transferring todot pattern data is completed upon completion of transfer of said dotpattern data to all of said plurality of memory devices.
 6. A method asclaimed in claim 1, wherein said step of producing said plurality ofcharged particle beams includes a step of parallel-to-serial conversionfor converting parallel dot pattern read out from said second storagedevice to serial dot pattern.
 7. A method as claimed in claim 6, whereinsaid step of producing said plurality of charged particle beams includesa step for delaying said serial dot pattern data collectively for onechannel included in said plurality of channels with respect to said dotpattern data for other channels in said plurality of channels.
 8. Amethod as claimed in claim 7, wherein said step of producing saidplurality of charged particle beams further includes a step of delaying,in each of said plurality of channels, said serial dot pattern data foractivating an aperture on said blanking aperture array, with respect tosaid serial dot pattern data that activates another aperture on saidblanking aperture array.
 9. A method as claimed in claim 8, wherein saidstep of producing the plurality of charged particle beams includes aphase adjusting step for adjusting a phase of said serial dot patterndata with respect to an exposure clock.
 10. A method as claimed in claim1, wherein said step of reading is conducted independently to said stepof producing the plurality of charged particle beams.
 11. A method asclaimed in claim 1, wherein said step of producing the plurality ofcharged particle beams includes a step of inverting the logic value ofsaid dot pattern data.
 12. A charged-particle-beam exposure system,comprising:beam source means for producing a charged particle beam andfor emitting the same along an optical axis in the form of a chargedparticle beam toward an object; beam shaping means disposed on saidoptical axis so as to interrupt said primary charged particle beam, saidbeam shaping means carrying thereon a plurality of apertures eachsupplied with exposure dot data representing a dot pattern to be exposedon said object, said apertures thereby shaping said charged particlebeam into a plurality of charged particle beam elements in response tosaid exposure dot data, said plurality of charged particle beam elementsas a whole forming a charged particle beam bundle; focusing means forfocusing each of said charged particle beam elements in said chargedparticle beam bundle upon said object with a demagnification; primarystorage means for storing said exposure dot data, said primary storagemeans having a first access speed; secondary storage means for storingsaid exposure dot data, said secondary storage means having a secondaccess speed substantially higher than said first access speed; and datatransfer means for transferring said dot pattern data from said primarystorage means to said secondary storage means; said secondary storagemeans supplying said dot pattern data therein to beam shaping means. 13.A charged particle beam exposure system as claimed in claim 12, whereinsaid secondary storage means comprises a memory device having an accessspeed substantially larger than that of said first storage means.
 14. Acharged particle beam exposure system as claimed in claim 12, whereinsaid secondary storage means is provided in a plural number incorrespondence to a plurality of channels, each channel corresponding toa group of the apertures on said beam shaping means that are suppliedwith identical dot pattern data, such that identical dot pattern data issupplied, in each channel, to a plurality of apertures included in saidapertures on said beam shaping means from said secondary storage means.15. A charged particle beam exposure system as claimed in claim 14,further including first delay means provided between said secondarystorage means and said beam shaping means for delaying said dot patterndata read out from said secondary storage means and supplied to saidbeam shaping means collectively for one channel, which channel isincluded in said plurality of channels, with respect to said dot patterndata for other channels in said plurality of channels.
 16. A chargedparticle beam exposure system as claimed in claim 15, further includingsecond delay means provided for each channel for delaying said dotpattern data, experienced a delay in said first delay means, for anaperture corresponding to said channel with respect to another aperturealso corresponding to said channel.
 17. A charged particle beam exposuresystem as claimed in claim 12, wherein a pair of storage devices areprovided for each channel as said secondary storage means, said datatransfer means causes a data transfer of dot pattern data from one ofsaid storage devices to said beam shaping means, said data transfermeans further causes a data transfer of dot pattern data from saidprimary storage means to the other of said storage devices, wherein saiddata transfer means carries out said data transfer from said primarystorage means to the other of said storage devices while carrying cutsimultaneously said data transfer from said one of said storage devicesto said beam shaping means.
 18. A charged particle beam exposure systemas claimed in claim 12, wherein said data transfer means produces acompletion signal indicative of completion of the data transfer to saidsecondary storage means upon completion of data transfer of all of thedot pattern data.
 19. A charged particle beam exposure system as claimedin claim 12, further including parallel-to-serial conversion meansprovided between said secondary storage means and said beam shapingmeans for converting said dot pattern data supplied from said secondarystorage means to said beam shaping means into serial dot pattern data.20. A charged particle beam exposure system as claimed in claim 19,further including inversion means provided between saidparallel-to-serial conversion means and said beam shaping means forinverting said serial dot pattern produced by said parallel-to-serialconversion means.
 21. A charged particle beam exposure system as claimedin claim 12, further including phase correction means between saidsecondary storage means and said beam shaping means for correcting thephase of said dot pattern data supplied from said secondary storagemeans to said beam shaping means.